--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/CSP2/CSP2_env/env-d9b9114564458d9d-741b3de822f2aaca6c6caa4325c4afce/include/kj/common.h	Tue Mar 18 17:55:14 2025 -0400
@@ -0,0 +1,2045 @@
+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+// Header that should be #included by everyone.
+//
+// This defines very simple utilities that are widely applicable.
+
+#pragma once
+
+#if defined(__GNUC__) || defined(__clang__)
+#define KJ_BEGIN_SYSTEM_HEADER _Pragma("GCC system_header")
+#elif defined(_MSC_VER)
+#define KJ_BEGIN_SYSTEM_HEADER __pragma(warning(push, 0))
+#define KJ_END_SYSTEM_HEADER __pragma(warning(pop))
+#endif
+
+#ifndef KJ_BEGIN_SYSTEM_HEADER
+#define KJ_BEGIN_SYSTEM_HEADER
+#endif
+
+#ifndef KJ_END_SYSTEM_HEADER
+#define KJ_END_SYSTEM_HEADER
+#endif
+
+#if !defined(KJ_HEADER_WARNINGS) || !KJ_HEADER_WARNINGS
+#define KJ_BEGIN_HEADER KJ_BEGIN_SYSTEM_HEADER
+#define KJ_END_HEADER KJ_END_SYSTEM_HEADER
+#else
+#define KJ_BEGIN_HEADER
+#define KJ_END_HEADER
+#endif
+
+#ifdef __has_cpp_attribute
+#define KJ_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
+#else
+#define KJ_HAS_CPP_ATTRIBUTE(x) 0
+#endif
+
+#ifdef __has_feature
+#define KJ_HAS_COMPILER_FEATURE(x) __has_feature(x)
+#else
+#define KJ_HAS_COMPILER_FEATURE(x) 0
+#endif
+
+#if defined(_MSVC_LANG) && !defined(__clang__)
+#define KJ_CPP_STD _MSVC_LANG
+#else
+#define KJ_CPP_STD __cplusplus
+#endif
+
+KJ_BEGIN_HEADER
+
+#ifndef KJ_NO_COMPILER_CHECK
+// Technically, __cplusplus should be 201402L for C++14, but GCC 4.9 -- which is supported -- still
+// had it defined to 201300L even with -std=c++14.
+#if KJ_CPP_STD < 201300L && !__CDT_PARSER__
+  #error "This code requires C++14. Either your compiler does not support it or it is not enabled."
+  #ifdef __GNUC__
+    // Compiler claims compatibility with GCC, so presumably supports -std.
+    #error "Pass -std=c++14 on the compiler command line to enable C++14."
+  #endif
+#endif
+
+#ifdef __GNUC__
+  #if __clang__
+    #if __clang_major__ < 5
+      #warning "This library requires at least Clang 5.0."
+    #elif KJ_CPP_STD >= 201402L && !__has_include(<initializer_list>)
+      #warning "Your compiler supports C++14 but your C++ standard library does not.  If your "\
+               "system has libc++ installed (as should be the case on e.g. Mac OSX), try adding "\
+               "-stdlib=libc++ to your CXXFLAGS."
+    #endif
+  #else
+    #if __GNUC__ < 5
+      #warning "This library requires at least GCC 5.0."
+    #endif
+  #endif
+#elif defined(_MSC_VER)
+  #if _MSC_VER < 1910 && !defined(__clang__)
+    #error "You need Visual Studio 2017 or better to compile this code."
+  #endif
+#else
+  #warning "I don't recognize your compiler. As of this writing, Clang, GCC, and Visual Studio "\
+           "are the only known compilers with enough C++14 support for this library. "\
+           "#define KJ_NO_COMPILER_CHECK to make this warning go away."
+#endif
+#endif
+
+#include <stddef.h>
+#include <cstring>
+#include <initializer_list>
+#include <string.h>
+
+#if __linux__ && KJ_CPP_STD > 201200L
+// Hack around stdlib bug with C++14 that exists on some Linux systems.
+// Apparently in this mode the C library decides not to define gets() but the C++ library still
+// tries to import it into the std namespace. This bug has been fixed at the source but is still
+// widely present in the wild e.g. on Ubuntu 14.04.
+#undef _GLIBCXX_HAVE_GETS
+#endif
+
+#if _WIN32
+// Windows likes to define macros for min() and max(). We just can't deal with this.
+// If windows.h was included already, undef these.
+#undef min
+#undef max
+// If windows.h was not included yet, define the macro that prevents min() and max() from being
+// defined.
+#ifndef NOMINMAX
+#define NOMINMAX 1
+#endif
+#endif
+
+#if defined(_MSC_VER)
+#include <intrin.h>  // __popcnt
+#endif
+
+// =======================================================================================
+
+namespace kj {
+
+typedef unsigned int uint;
+typedef unsigned char byte;
+
+// =======================================================================================
+// Common macros, especially for common yet compiler-specific features.
+
+// Detect whether RTTI and exceptions are enabled, assuming they are unless we have specific
+// evidence to the contrary.  Clients can always define KJ_NO_RTTI or KJ_NO_EXCEPTIONS explicitly
+// to override these checks.
+
+// TODO: Ideally we'd use __cpp_exceptions/__cpp_rtti not being defined as the first pass since
+//   that is the standard compliant way. However, it's unclear how to use those macros (or any
+//   others) to distinguish between the compiler supporting feature detection and the feature being
+//   disabled vs the compiler not supporting feature detection at all.
+#if defined(__has_feature)
+  #if !defined(KJ_NO_RTTI) && !__has_feature(cxx_rtti)
+    #define KJ_NO_RTTI 1
+  #endif
+  #if !defined(KJ_NO_EXCEPTIONS) && !__has_feature(cxx_exceptions)
+    #define KJ_NO_EXCEPTIONS 1
+  #endif
+#elif defined(__GNUC__)
+  #if !defined(KJ_NO_RTTI) && !__GXX_RTTI
+    #define KJ_NO_RTTI 1
+  #endif
+  #if !defined(KJ_NO_EXCEPTIONS) && !__EXCEPTIONS
+    #define KJ_NO_EXCEPTIONS 1
+  #endif
+#elif defined(_MSC_VER)
+  #if !defined(KJ_NO_RTTI) && !defined(_CPPRTTI)
+    #define KJ_NO_RTTI 1
+  #endif
+  #if !defined(KJ_NO_EXCEPTIONS) && !defined(_CPPUNWIND)
+    #define KJ_NO_EXCEPTIONS 1
+  #endif
+#endif
+
+#if !defined(KJ_DEBUG) && !defined(KJ_NDEBUG)
+// Heuristically decide whether to enable debug mode.  If DEBUG or NDEBUG is defined, use that.
+// Otherwise, fall back to checking whether optimization is enabled.
+#if defined(DEBUG) || defined(_DEBUG)
+#define KJ_DEBUG
+#elif defined(NDEBUG)
+#define KJ_NDEBUG
+#elif __OPTIMIZE__
+#define KJ_NDEBUG
+#else
+#define KJ_DEBUG
+#endif
+#endif
+
+#define KJ_DISALLOW_COPY(classname) \
+  classname(const classname&) = delete; \
+  classname& operator=(const classname&) = delete
+// Deletes the implicit copy constructor and assignment operator. This inhibits the compiler from
+// generating the implicit move constructor and assignment operator for this class, but allows the
+// code author to supply them, if they make sense to implement.
+//
+// This macro should not be your first choice. Instead, prefer using KJ_DISALLOW_COPY_AND_MOVE, and only use
+// this macro when you have determined that you must implement move semantics for your type.
+
+#define KJ_DISALLOW_COPY_AND_MOVE(classname) \
+  classname(const classname&) = delete; \
+  classname& operator=(const classname&) = delete; \
+  classname(classname&&) = delete; \
+  classname& operator=(classname&&) = delete
+// Deletes the implicit copy and move constructors and assignment operators. This is useful in cases
+// where the code author wants to provide an additional compile-time guard against subsequent
+// maintainers casually adding move operations. This is particularly useful when implementing RAII
+// classes that are intended to be completely immobile.
+
+#ifdef __GNUC__
+#define KJ_LIKELY(condition) __builtin_expect(condition, true)
+#define KJ_UNLIKELY(condition) __builtin_expect(condition, false)
+// Branch prediction macros.  Evaluates to the condition given, but also tells the compiler that we
+// expect the condition to be true/false enough of the time that it's worth hard-coding branch
+// prediction.
+#else
+#define KJ_LIKELY(condition) (condition)
+#define KJ_UNLIKELY(condition) (condition)
+#endif
+
+#if defined(KJ_DEBUG) || __NO_INLINE__
+#define KJ_ALWAYS_INLINE(...) inline __VA_ARGS__
+// Don't force inline in debug mode.
+#else
+#if defined(_MSC_VER) && !defined(__clang__)
+#define KJ_ALWAYS_INLINE(...) __forceinline __VA_ARGS__
+#else
+#define KJ_ALWAYS_INLINE(...) inline __VA_ARGS__ __attribute__((always_inline))
+#endif
+// Force a function to always be inlined.  Apply only to the prototype, not to the definition.
+#endif
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#define KJ_NOINLINE __declspec(noinline)
+#else
+#define KJ_NOINLINE __attribute__((noinline))
+#endif
+
+#if defined(_MSC_VER) && !__clang__
+#define KJ_NORETURN(prototype) __declspec(noreturn) prototype
+#define KJ_UNUSED
+#define KJ_WARN_UNUSED_RESULT
+// TODO(msvc): KJ_WARN_UNUSED_RESULT can use _Check_return_ on MSVC, but it's a prefix, so
+//   wrapping the whole prototype is needed. http://msdn.microsoft.com/en-us/library/jj159529.aspx
+//   Similarly, KJ_UNUSED could use __pragma(warning(suppress:...)), but again that's a prefix.
+#else
+#define KJ_NORETURN(prototype) prototype __attribute__((noreturn))
+#define KJ_UNUSED __attribute__((unused))
+#define KJ_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
+#endif
+
+#if KJ_HAS_CPP_ATTRIBUTE(clang::lifetimebound)
+// If this is generating too many false-positives, the user is responsible for disabling the
+// problematic warning at the compiler switch level or by suppressing the place where the
+// false-positive is reported through compiler-specific pragmas if available.
+#define KJ_LIFETIMEBOUND [[clang::lifetimebound]]
+#else
+#define KJ_LIFETIMEBOUND
+#endif
+// Annotation that indicates the returned value is referencing a resource owned by this type (e.g.
+// cStr() on a std::string). Unfortunately this lifetime can only be superficial currently & cannot
+// track further. For example, there's no way to get `array.asPtr().slice(5, 6))` to warn if the
+// last slice exceeds the lifetime of `array`. That's because in the general case `ArrayPtr::slice`
+// can't have the lifetime bound annotation since it's not wrong to do something like:
+//     ArrayPtr<char> doSomething(ArrayPtr<char> foo) {
+//        ...
+//        return foo.slice(5, 6);
+//     }
+// If `ArrayPtr::slice` had a lifetime bound then the compiler would warn about this perfectly
+// legitimate method. Really there needs to be 2 more annotations. One to inherit the lifetime bound
+// and another to inherit the lifetime bound from a parameter (which really could be the same thing
+// by allowing a syntax like `[[clang::lifetimebound(*this)]]`.
+// https://clang.llvm.org/docs/AttributeReference.html#lifetimebound
+
+#if __clang__
+#define KJ_UNUSED_MEMBER __attribute__((unused))
+// Inhibits "unused" warning for member variables.  Only Clang produces such a warning, while GCC
+// complains if the attribute is set on members.
+#else
+#define KJ_UNUSED_MEMBER
+#endif
+
+#if KJ_CPP_STD > 201703L || (__clang__  && __clang_major__ >= 9 && KJ_CPP_STD >= 201103L)
+// Technically this was only added to C++20 but Clang allows it for >= C++11 and spelunking the
+// attributes manual indicates it first came in with Clang 9.
+#define KJ_NO_UNIQUE_ADDRESS [[no_unique_address]]
+#else
+#define KJ_NO_UNIQUE_ADDRESS
+#endif
+
+#if KJ_HAS_COMPILER_FEATURE(thread_sanitizer) || defined(__SANITIZE_THREAD__)
+#define KJ_DISABLE_TSAN __attribute__((no_sanitize("thread"), noinline))
+#else
+#define KJ_DISABLE_TSAN
+#endif
+
+#if __clang__
+#define KJ_DEPRECATED(reason) \
+    __attribute__((deprecated(reason)))
+#define KJ_UNAVAILABLE(reason) \
+    __attribute__((unavailable(reason)))
+#elif __GNUC__
+#define KJ_DEPRECATED(reason) \
+    __attribute__((deprecated))
+#define KJ_UNAVAILABLE(reason) = delete
+// If the `unavailable` attribute is not supproted, just mark the method deleted, which at least
+// makes it a compile-time error to try to call it. Note that on Clang, marking a method deleted
+// *and* unavailable unfortunately defeats the purpose of the unavailable annotation, as the
+// generic "deleted" error is reported instead.
+#else
+#define KJ_DEPRECATED(reason)
+#define KJ_UNAVAILABLE(reason) = delete
+// TODO(msvc): Again, here, MSVC prefers a prefix, __declspec(deprecated).
+#endif
+
+#if KJ_TESTING_KJ  // defined in KJ's own unit tests; others should not define this
+#undef KJ_DEPRECATED
+#define KJ_DEPRECATED(reason)
+#endif
+
+namespace _ {  // private
+
+KJ_NORETURN(void inlineRequireFailure(
+    const char* file, int line, const char* expectation, const char* macroArgs,
+    const char* message = nullptr));
+
+KJ_NORETURN(void unreachable());
+
+}  // namespace _ (private)
+
+#if _MSC_VER && !defined(__clang__) && (!defined(_MSVC_TRADITIONAL) || _MSVC_TRADITIONAL)
+#define KJ_MSVC_TRADITIONAL_CPP 1
+#endif
+
+#ifdef KJ_DEBUG
+#if KJ_MSVC_TRADITIONAL_CPP
+#define KJ_IREQUIRE(condition, ...) \
+    if (KJ_LIKELY(condition)); else ::kj::_::inlineRequireFailure( \
+        __FILE__, __LINE__, #condition, "" #__VA_ARGS__, __VA_ARGS__)
+// Version of KJ_DREQUIRE() which is safe to use in headers that are #included by users.  Used to
+// check preconditions inside inline methods.  KJ_IREQUIRE is particularly useful in that
+// it will be enabled depending on whether the application is compiled in debug mode rather than
+// whether libkj is.
+#else
+#define KJ_IREQUIRE(condition, ...) \
+    if (KJ_LIKELY(condition)); else ::kj::_::inlineRequireFailure( \
+        __FILE__, __LINE__, #condition, #__VA_ARGS__, ##__VA_ARGS__)
+// Version of KJ_DREQUIRE() which is safe to use in headers that are #included by users.  Used to
+// check preconditions inside inline methods.  KJ_IREQUIRE is particularly useful in that
+// it will be enabled depending on whether the application is compiled in debug mode rather than
+// whether libkj is.
+#endif
+#else
+#define KJ_IREQUIRE(condition, ...)
+#endif
+
+#define KJ_IASSERT KJ_IREQUIRE
+
+#define KJ_UNREACHABLE ::kj::_::unreachable();
+// Put this on code paths that cannot be reached to suppress compiler warnings about missing
+// returns.
+
+#if __clang__
+#define KJ_CLANG_KNOWS_THIS_IS_UNREACHABLE_BUT_GCC_DOESNT
+#else
+#define KJ_CLANG_KNOWS_THIS_IS_UNREACHABLE_BUT_GCC_DOESNT KJ_UNREACHABLE
+#endif
+
+#if __clang__
+#define KJ_KNOWN_UNREACHABLE(code) \
+    do { \
+      _Pragma("clang diagnostic push") \
+      _Pragma("clang diagnostic ignored \"-Wunreachable-code\"") \
+      code; \
+      _Pragma("clang diagnostic pop") \
+    } while (false)
+// Suppress "unreachable code" warnings on intentionally unreachable code.
+#else
+// TODO(someday): Add support for non-clang compilers.
+#define KJ_KNOWN_UNREACHABLE(code) do {code;} while(false)
+#endif
+
+#if KJ_HAS_CPP_ATTRIBUTE(fallthrough)
+#define KJ_FALLTHROUGH [[fallthrough]]
+#else
+#define KJ_FALLTHROUGH
+#endif
+
+// #define KJ_STACK_ARRAY(type, name, size, minStack, maxStack)
+//
+// Allocate an array, preferably on the stack, unless it is too big.  On GCC this will use
+// variable-sized arrays.  For other compilers we could just use a fixed-size array.  `minStack`
+// is the stack array size to use if variable-width arrays are not supported.  `maxStack` is the
+// maximum stack array size if variable-width arrays *are* supported.
+#if __GNUC__ && !__clang__
+#define KJ_STACK_ARRAY(type, name, size, minStack, maxStack) \
+  size_t name##_size = (size); \
+  bool name##_isOnStack = name##_size <= (maxStack); \
+  type name##_stack[kj::max(1, name##_isOnStack ? name##_size : 0)]; \
+  ::kj::Array<type> name##_heap = name##_isOnStack ? \
+      nullptr : kj::heapArray<type>(name##_size); \
+  ::kj::ArrayPtr<type> name = name##_isOnStack ? \
+      kj::arrayPtr(name##_stack, name##_size) : name##_heap
+#else
+#define KJ_STACK_ARRAY(type, name, size, minStack, maxStack) \
+  size_t name##_size = (size); \
+  bool name##_isOnStack = name##_size <= (minStack); \
+  type name##_stack[minStack]; \
+  ::kj::Array<type> name##_heap = name##_isOnStack ? \
+      nullptr : kj::heapArray<type>(name##_size); \
+  ::kj::ArrayPtr<type> name = name##_isOnStack ? \
+      kj::arrayPtr(name##_stack, name##_size) : name##_heap
+#endif
+
+#define KJ_CONCAT_(x, y) x##y
+#define KJ_CONCAT(x, y) KJ_CONCAT_(x, y)
+#define KJ_UNIQUE_NAME(prefix) KJ_CONCAT(prefix, __LINE__)
+// Create a unique identifier name.  We use concatenate __LINE__ rather than __COUNTER__ so that
+// the name can be used multiple times in the same macro.
+
+#if _MSC_VER && !defined(__clang__)
+
+#define KJ_CONSTEXPR(...) __VA_ARGS__
+// Use in cases where MSVC barfs on constexpr. A replacement keyword (e.g. "const") can be
+// provided, or just leave blank to remove the keyword entirely.
+//
+// TODO(msvc): Remove this hack once MSVC fully supports constexpr.
+
+#ifndef __restrict__
+#define __restrict__ __restrict
+// TODO(msvc): Would it be better to define a KJ_RESTRICT macro?
+#endif
+
+#pragma warning(disable: 4521 4522)
+// This warning complains when there are two copy constructors, one for a const reference and
+// one for a non-const reference. It is often quite necessary to do this in wrapper templates,
+// therefore this warning is dumb and we disable it.
+
+#pragma warning(disable: 4458)
+// Warns when a parameter name shadows a class member. Unfortunately my code does this a lot,
+// since I don't use a special name format for members.
+
+#else  // _MSC_VER
+#define KJ_CONSTEXPR(...) constexpr
+#endif
+
+// =======================================================================================
+// Template metaprogramming helpers.
+
+#define KJ_HAS_TRIVIAL_CONSTRUCTOR __is_trivially_constructible
+#if __GNUC__ && !__clang__
+#define KJ_HAS_NOTHROW_CONSTRUCTOR __has_nothrow_constructor
+#define KJ_HAS_TRIVIAL_DESTRUCTOR __has_trivial_destructor
+#else
+#define KJ_HAS_NOTHROW_CONSTRUCTOR __is_nothrow_constructible
+#define KJ_HAS_TRIVIAL_DESTRUCTOR __is_trivially_destructible
+#endif
+
+template <typename T> struct NoInfer_ { typedef T Type; };
+template <typename T> using NoInfer = typename NoInfer_<T>::Type;
+// Use NoInfer<T>::Type in place of T for a template function parameter to prevent inference of
+// the type based on the parameter value.
+
+template <typename T> struct RemoveConst_ { typedef T Type; };
+template <typename T> struct RemoveConst_<const T> { typedef T Type; };
+template <typename T> using RemoveConst = typename RemoveConst_<T>::Type;
+
+template <typename> struct IsLvalueReference_ { static constexpr bool value = false; };
+template <typename T> struct IsLvalueReference_<T&> { static constexpr bool value = true; };
+template <typename T>
+inline constexpr bool isLvalueReference() { return IsLvalueReference_<T>::value; }
+
+template <typename T> struct Decay_ { typedef T Type; };
+template <typename T> struct Decay_<T&> { typedef typename Decay_<T>::Type Type; };
+template <typename T> struct Decay_<T&&> { typedef typename Decay_<T>::Type Type; };
+template <typename T> struct Decay_<T[]> { typedef typename Decay_<T*>::Type Type; };
+template <typename T> struct Decay_<const T[]> { typedef typename Decay_<const T*>::Type Type; };
+template <typename T, size_t s> struct Decay_<T[s]> { typedef typename Decay_<T*>::Type Type; };
+template <typename T, size_t s> struct Decay_<const T[s]> { typedef typename Decay_<const T*>::Type Type; };
+template <typename T> struct Decay_<const T> { typedef typename Decay_<T>::Type Type; };
+template <typename T> struct Decay_<volatile T> { typedef typename Decay_<T>::Type Type; };
+template <typename T> using Decay = typename Decay_<T>::Type;
+
+template <bool b> struct EnableIf_;
+template <> struct EnableIf_<true> { typedef void Type; };
+template <bool b> using EnableIf = typename EnableIf_<b>::Type;
+// Use like:
+//
+//     template <typename T, typename = EnableIf<isValid<T>()>>
+//     void func(T&& t);
+
+template <typename...> struct VoidSfinae_ { using Type = void; };
+template <typename... Ts> using VoidSfinae = typename VoidSfinae_<Ts...>::Type;
+// Note: VoidSfinae is std::void_t from C++17.
+
+template <typename T>
+T instance() noexcept;
+// Like std::declval, but doesn't transform T into an rvalue reference.  If you want that, specify
+// instance<T&&>().
+
+struct DisallowConstCopy {
+  // Inherit from this, or declare a member variable of this type, to prevent the class from being
+  // copyable from a const reference -- instead, it will only be copyable from non-const references.
+  // This is useful for enforcing transitive constness of contained pointers.
+  //
+  // For example, say you have a type T which contains a pointer.  T has non-const methods which
+  // modify the value at that pointer, but T's const methods are designed to allow reading only.
+  // Unfortunately, if T has a regular copy constructor, someone can simply make a copy of T and
+  // then use it to modify the pointed-to value.  However, if T inherits DisallowConstCopy, then
+  // callers will only be able to copy non-const instances of T.  Ideally, there is some
+  // parallel type ImmutableT which is like a version of T that only has const methods, and can
+  // be copied from a const T.
+  //
+  // Note that due to C++ rules about implicit copy constructors and assignment operators, any
+  // type that contains or inherits from a type that disallows const copies will also automatically
+  // disallow const copies.  Hey, cool, that's exactly what we want.
+
+#if CAPNP_DEBUG_TYPES
+  // Alas! Declaring a defaulted non-const copy constructor tickles a bug which causes GCC and
+  // Clang to disagree on ABI, using different calling conventions to pass this type, leading to
+  // immediate segfaults. See:
+  //     https://bugs.llvm.org/show_bug.cgi?id=23764
+  //     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58074
+  //
+  // Because of this, we can't use this technique. We guard it by CAPNP_DEBUG_TYPES so that it
+  // still applies to the Cap'n Proto developers during internal testing.
+
+  DisallowConstCopy() = default;
+  DisallowConstCopy(DisallowConstCopy&) = default;
+  DisallowConstCopy(DisallowConstCopy&&) = default;
+  DisallowConstCopy& operator=(DisallowConstCopy&) = default;
+  DisallowConstCopy& operator=(DisallowConstCopy&&) = default;
+#endif
+};
+
+#if _MSC_VER && !defined(__clang__)
+
+#define KJ_CPCAP(obj) obj=::kj::cp(obj)
+// TODO(msvc): MSVC refuses to invoke non-const versions of copy constructors in by-value lambda
+// captures. Wrap your captured object in this macro to force the compiler to perform a copy.
+// Example:
+//
+//   struct Foo: DisallowConstCopy {};
+//   Foo foo;
+//   auto lambda = [KJ_CPCAP(foo)] {};
+
+#else
+
+#define KJ_CPCAP(obj) obj
+// Clang and gcc both already perform copy capturing correctly with non-const copy constructors.
+
+#endif
+
+template <typename T>
+struct DisallowConstCopyIfNotConst: public DisallowConstCopy {
+  // Inherit from this when implementing a template that contains a pointer to T and which should
+  // enforce transitive constness.  If T is a const type, this has no effect.  Otherwise, it is
+  // an alias for DisallowConstCopy.
+};
+
+template <typename T>
+struct DisallowConstCopyIfNotConst<const T> {};
+
+template <typename T> struct IsConst_ { static constexpr bool value = false; };
+template <typename T> struct IsConst_<const T> { static constexpr bool value = true; };
+template <typename T> constexpr bool isConst() { return IsConst_<T>::value; }
+
+template <typename T> struct EnableIfNotConst_ { typedef T Type; };
+template <typename T> struct EnableIfNotConst_<const T>;
+template <typename T> using EnableIfNotConst = typename EnableIfNotConst_<T>::Type;
+
+template <typename T> struct EnableIfConst_;
+template <typename T> struct EnableIfConst_<const T> { typedef T Type; };
+template <typename T> using EnableIfConst = typename EnableIfConst_<T>::Type;
+
+template <typename T> struct RemoveConstOrDisable_ { struct Type; };
+template <typename T> struct RemoveConstOrDisable_<const T> { typedef T Type; };
+template <typename T> using RemoveConstOrDisable = typename RemoveConstOrDisable_<T>::Type;
+
+template <typename T> struct IsReference_ { static constexpr bool value = false; };
+template <typename T> struct IsReference_<T&> { static constexpr bool value = true; };
+template <typename T> constexpr bool isReference() { return IsReference_<T>::value; }
+
+template <typename From, typename To>
+struct PropagateConst_ { typedef To Type; };
+template <typename From, typename To>
+struct PropagateConst_<const From, To> { typedef const To Type; };
+template <typename From, typename To>
+using PropagateConst = typename PropagateConst_<From, To>::Type;
+
+namespace _ {  // private
+
+template <typename T>
+T refIfLvalue(T&&);
+
+}  // namespace _ (private)
+
+#define KJ_DECLTYPE_REF(exp) decltype(::kj::_::refIfLvalue(exp))
+// Like decltype(exp), but if exp is an lvalue, produces a reference type.
+//
+//     int i;
+//     decltype(i) i1(i);                         // i1 has type int.
+//     KJ_DECLTYPE_REF(i + 1) i2(i + 1);          // i2 has type int.
+//     KJ_DECLTYPE_REF(i) i3(i);                  // i3 has type int&.
+//     KJ_DECLTYPE_REF(kj::mv(i)) i4(kj::mv(i));  // i4 has type int.
+
+template <typename T, typename U> struct IsSameType_ { static constexpr bool value = false; };
+template <typename T> struct IsSameType_<T, T> { static constexpr bool value = true; };
+template <typename T, typename U> constexpr bool isSameType() { return IsSameType_<T, U>::value; }
+
+template <typename T> constexpr bool isIntegral() { return false; }
+template <> constexpr bool isIntegral<char>() { return true; }
+template <> constexpr bool isIntegral<signed char>() { return true; }
+template <> constexpr bool isIntegral<short>() { return true; }
+template <> constexpr bool isIntegral<int>() { return true; }
+template <> constexpr bool isIntegral<long>() { return true; }
+template <> constexpr bool isIntegral<long long>() { return true; }
+template <> constexpr bool isIntegral<unsigned char>() { return true; }
+template <> constexpr bool isIntegral<unsigned short>() { return true; }
+template <> constexpr bool isIntegral<unsigned int>() { return true; }
+template <> constexpr bool isIntegral<unsigned long>() { return true; }
+template <> constexpr bool isIntegral<unsigned long long>() { return true; }
+
+template <typename T>
+struct CanConvert_ {
+  static int sfinae(T);
+  static bool sfinae(...);
+};
+
+template <typename T, typename U>
+constexpr bool canConvert() {
+  return sizeof(CanConvert_<U>::sfinae(instance<T>())) == sizeof(int);
+}
+
+#if __GNUC__ && !__clang__ && __GNUC__ < 5
+template <typename T>
+constexpr bool canMemcpy() {
+  // Returns true if T can be copied using memcpy instead of using the copy constructor or
+  // assignment operator.
+
+  // GCC 4 does not have __is_trivially_constructible and friends, and there doesn't seem to be
+  // any reliable alternative. __has_trivial_copy() and __has_trivial_assign() return the right
+  // thing at one point but later on they changed such that a deleted copy constructor was
+  // considered "trivial" (apparently technically correct, though useless). So, on GCC 4 we give up
+  // and assume we can't memcpy() at all, and must explicitly copy-construct everything.
+  return false;
+}
+#define KJ_ASSERT_CAN_MEMCPY(T)
+#else
+template <typename T>
+constexpr bool canMemcpy() {
+  // Returns true if T can be copied using memcpy instead of using the copy constructor or
+  // assignment operator.
+
+  return __is_trivially_constructible(T, const T&) && __is_trivially_assignable(T, const T&);
+}
+#define KJ_ASSERT_CAN_MEMCPY(T) \
+  static_assert(kj::canMemcpy<T>(), "this code expects this type to be memcpy()-able");
+#endif
+
+template <typename T>
+class Badge {
+  // A pattern for marking individual methods such that they can only be called from a specific
+  // caller class: Make the method public but give it a parameter of type `Badge<Caller>`. Only
+  // `Caller` can construct one, so only `Caller` can call the method.
+  //
+  //     // We only allow calls from the class `Bar`.
+  //     void foo(Badge<Bar>)
+  //
+  // The call site looks like:
+  //
+  //     foo({});
+  //
+  // This pattern also works well for declaring private constructors, but still being able to use
+  // them with `kj::heap()`, etc.
+  //
+  // Idea from: https://awesomekling.github.io/Serenity-C++-patterns-The-Badge/
+  //
+  // Note that some forms of this idea make the copy constructor private as well, in order to
+  // prohibit `Badge<NotMe>(*(Badge<NotMe>*)nullptr)`. However, that would prevent badges from
+  // being passed through forwarding functions like `kj::heap()`, which would ruin one of the main
+  // use cases for this pattern in KJ. In any case, dereferencing a null pointer is UB; there are
+  // plenty of other ways to get access to private members if you're willing to go UB. For one-off
+  // debugging purposes, you might as well use `#define private public` at the top of the file.
+private:
+  Badge() {}
+  friend T;
+};
+
+// =======================================================================================
+// Equivalents to std::move() and std::forward(), since these are very commonly needed and the
+// std header <utility> pulls in lots of other stuff.
+//
+// We use abbreviated names mv and fwd because these helpers (especially mv) are so commonly used
+// that the cost of typing more letters outweighs the cost of being slightly harder to understand
+// when first encountered.
+
+template<typename T> constexpr T&& mv(T& t) noexcept { return static_cast<T&&>(t); }
+template<typename T> constexpr T&& fwd(NoInfer<T>& t) noexcept { return static_cast<T&&>(t); }
+
+template<typename T> constexpr T cp(T& t) noexcept { return t; }
+template<typename T> constexpr T cp(const T& t) noexcept { return t; }
+// Useful to force a copy, particularly to pass into a function that expects T&&.
+
+template <typename T, typename U, bool takeT, bool uOK = true> struct ChooseType_;
+template <typename T, typename U> struct ChooseType_<T, U, true, true> { typedef T Type; };
+template <typename T, typename U> struct ChooseType_<T, U, true, false> { typedef T Type; };
+template <typename T, typename U> struct ChooseType_<T, U, false, true> { typedef U Type; };
+
+template <typename T, typename U>
+using WiderType = typename ChooseType_<T, U, sizeof(T) >= sizeof(U)>::Type;
+
+template <typename T, typename U>
+inline constexpr auto min(T&& a, U&& b) -> WiderType<Decay<T>, Decay<U>> {
+  return a < b ? WiderType<Decay<T>, Decay<U>>(a) : WiderType<Decay<T>, Decay<U>>(b);
+}
+
+template <typename T, typename U>
+inline constexpr auto max(T&& a, U&& b) -> WiderType<Decay<T>, Decay<U>> {
+  return a > b ? WiderType<Decay<T>, Decay<U>>(a) : WiderType<Decay<T>, Decay<U>>(b);
+}
+
+template <typename T, size_t s>
+inline constexpr size_t size(T (&arr)[s]) { return s; }
+template <typename T>
+inline constexpr size_t size(T&& arr) { return arr.size(); }
+// Returns the size of the parameter, whether the parameter is a regular C array or a container
+// with a `.size()` method.
+
+class MaxValue_ {
+private:
+  template <typename T>
+  inline constexpr T maxSigned() const {
+    return (1ull << (sizeof(T) * 8 - 1)) - 1;
+  }
+  template <typename T>
+  inline constexpr T maxUnsigned() const {
+    return ~static_cast<T>(0u);
+  }
+
+public:
+#define _kJ_HANDLE_TYPE(T) \
+  inline constexpr operator   signed T() const { return MaxValue_::maxSigned  <  signed T>(); } \
+  inline constexpr operator unsigned T() const { return MaxValue_::maxUnsigned<unsigned T>(); }
+  _kJ_HANDLE_TYPE(char)
+  _kJ_HANDLE_TYPE(short)
+  _kJ_HANDLE_TYPE(int)
+  _kJ_HANDLE_TYPE(long)
+  _kJ_HANDLE_TYPE(long long)
+#undef _kJ_HANDLE_TYPE
+
+  inline constexpr operator char() const {
+    // `char` is different from both `signed char` and `unsigned char`, and may be signed or
+    // unsigned on different platforms.  Ugh.
+    return char(-1) < 0 ? MaxValue_::maxSigned<char>()
+                        : MaxValue_::maxUnsigned<char>();
+  }
+};
+
+class MinValue_ {
+private:
+  template <typename T>
+  inline constexpr T minSigned() const {
+    return 1ull << (sizeof(T) * 8 - 1);
+  }
+  template <typename T>
+  inline constexpr T minUnsigned() const {
+    return 0u;
+  }
+
+public:
+#define _kJ_HANDLE_TYPE(T) \
+  inline constexpr operator   signed T() const { return MinValue_::minSigned  <  signed T>(); } \
+  inline constexpr operator unsigned T() const { return MinValue_::minUnsigned<unsigned T>(); }
+  _kJ_HANDLE_TYPE(char)
+  _kJ_HANDLE_TYPE(short)
+  _kJ_HANDLE_TYPE(int)
+  _kJ_HANDLE_TYPE(long)
+  _kJ_HANDLE_TYPE(long long)
+#undef _kJ_HANDLE_TYPE
+
+  inline constexpr operator char() const {
+    // `char` is different from both `signed char` and `unsigned char`, and may be signed or
+    // unsigned on different platforms.  Ugh.
+    return char(-1) < 0 ? MinValue_::minSigned<char>()
+                        : MinValue_::minUnsigned<char>();
+  }
+};
+
+static KJ_CONSTEXPR(const) MaxValue_ maxValue = MaxValue_();
+// A special constant which, when cast to an integer type, takes on the maximum possible value of
+// that type.  This is useful to use as e.g. a parameter to a function because it will be robust
+// in the face of changes to the parameter's type.
+//
+// `char` is not supported, but `signed char` and `unsigned char` are.
+
+static KJ_CONSTEXPR(const) MinValue_ minValue = MinValue_();
+// A special constant which, when cast to an integer type, takes on the minimum possible value
+// of that type.  This is useful to use as e.g. a parameter to a function because it will be robust
+// in the face of changes to the parameter's type.
+//
+// `char` is not supported, but `signed char` and `unsigned char` are.
+
+template <typename T>
+inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
+template <typename T>
+inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
+
+template <uint bits>
+inline constexpr unsigned long long maxValueForBits() {
+  // Get the maximum integer representable in the given number of bits.
+
+  // 1ull << 64 is unfortunately undefined.
+  return (bits == 64 ? 0 : (1ull << bits)) - 1;
+}
+
+struct ThrowOverflow {
+  // Functor which throws an exception complaining about integer overflow. Usually this is used
+  // with the interfaces in units.h, but is defined here because Cap'n Proto wants to avoid
+  // including units.h when not using CAPNP_DEBUG_TYPES.
+  [[noreturn]] void operator()() const;
+};
+
+#if __GNUC__ || __clang__ || _MSC_VER
+inline constexpr float inf() { return __builtin_huge_valf(); }
+inline constexpr float nan() { return __builtin_nanf(""); }
+
+#else
+#error "Not sure how to support your compiler."
+#endif
+
+inline constexpr bool isNaN(float f) { return f != f; }
+inline constexpr bool isNaN(double f) { return f != f; }
+
+inline int popCount(unsigned int x) {
+#if defined(_MSC_VER) && !defined(__clang__)
+  return __popcnt(x);
+  // Note: __popcnt returns unsigned int, but the value is clearly guaranteed to fit into an int
+#else
+  return __builtin_popcount(x);
+#endif
+}
+
+// =======================================================================================
+// Useful fake containers
+
+template <typename T>
+class Range {
+public:
+  inline constexpr Range(const T& begin, const T& end): begin_(begin), end_(end) {}
+  inline explicit constexpr Range(const T& end): begin_(0), end_(end) {}
+
+  class Iterator {
+  public:
+    Iterator() = default;
+    inline Iterator(const T& value): value(value) {}
+
+    inline const T&  operator* () const { return value; }
+    inline const T&  operator[](size_t index) const { return value + index; }
+    inline Iterator& operator++() { ++value; return *this; }
+    inline Iterator  operator++(int) { return Iterator(value++); }
+    inline Iterator& operator--() { --value; return *this; }
+    inline Iterator  operator--(int) { return Iterator(value--); }
+    inline Iterator& operator+=(ptrdiff_t amount) { value += amount; return *this; }
+    inline Iterator& operator-=(ptrdiff_t amount) { value -= amount; return *this; }
+    inline Iterator  operator+ (ptrdiff_t amount) const { return Iterator(value + amount); }
+    inline Iterator  operator- (ptrdiff_t amount) const { return Iterator(value - amount); }
+    inline ptrdiff_t operator- (const Iterator& other) const { return value - other.value; }
+
+    inline bool operator==(const Iterator& other) const { return value == other.value; }
+    inline bool operator!=(const Iterator& other) const { return value != other.value; }
+    inline bool operator<=(const Iterator& other) const { return value <= other.value; }
+    inline bool operator>=(const Iterator& other) const { return value >= other.value; }
+    inline bool operator< (const Iterator& other) const { return value <  other.value; }
+    inline bool operator> (const Iterator& other) const { return value >  other.value; }
+
+  private:
+    T value;
+  };
+
+  inline Iterator begin() const { return Iterator(begin_); }
+  inline Iterator end() const { return Iterator(end_); }
+
+  inline auto size() const -> decltype(instance<T>() - instance<T>()) { return end_ - begin_; }
+
+private:
+  T begin_;
+  T end_;
+};
+
+template <typename T, typename U>
+inline constexpr Range<WiderType<Decay<T>, Decay<U>>> range(T begin, U end) {
+  return Range<WiderType<Decay<T>, Decay<U>>>(begin, end);
+}
+
+template <typename T>
+inline constexpr Range<Decay<T>> range(T begin, T end) { return Range<Decay<T>>(begin, end); }
+// Returns a fake iterable container containing all values of T from `begin` (inclusive) to `end`
+// (exclusive).  Example:
+//
+//     // Prints 1, 2, 3, 4, 5, 6, 7, 8, 9.
+//     for (int i: kj::range(1, 10)) { print(i); }
+
+template <typename T>
+inline constexpr Range<Decay<T>> zeroTo(T end) { return Range<Decay<T>>(end); }
+// Returns a fake iterable container containing all values of T from zero (inclusive) to `end`
+// (exclusive).  Example:
+//
+//     // Prints 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
+//     for (int i: kj::zeroTo(10)) { print(i); }
+
+template <typename T>
+inline constexpr Range<size_t> indices(T&& container) {
+  // Shortcut for iterating over the indices of a container:
+  //
+  //     for (size_t i: kj::indices(myArray)) { handle(myArray[i]); }
+
+  return range<size_t>(0, kj::size(container));
+}
+
+template <typename T>
+class Repeat {
+public:
+  inline constexpr Repeat(const T& value, size_t count): value(value), count(count) {}
+
+  class Iterator {
+  public:
+    Iterator() = default;
+    inline Iterator(const T& value, size_t index): value(value), index(index) {}
+
+    inline const T&  operator* () const { return value; }
+    inline const T&  operator[](ptrdiff_t index) const { return value; }
+    inline Iterator& operator++() { ++index; return *this; }
+    inline Iterator  operator++(int) { return Iterator(value, index++); }
+    inline Iterator& operator--() { --index; return *this; }
+    inline Iterator  operator--(int) { return Iterator(value, index--); }
+    inline Iterator& operator+=(ptrdiff_t amount) { index += amount; return *this; }
+    inline Iterator& operator-=(ptrdiff_t amount) { index -= amount; return *this; }
+    inline Iterator  operator+ (ptrdiff_t amount) const { return Iterator(value, index + amount); }
+    inline Iterator  operator- (ptrdiff_t amount) const { return Iterator(value, index - amount); }
+    inline ptrdiff_t operator- (const Iterator& other) const { return index - other.index; }
+
+    inline bool operator==(const Iterator& other) const { return index == other.index; }
+    inline bool operator!=(const Iterator& other) const { return index != other.index; }
+    inline bool operator<=(const Iterator& other) const { return index <= other.index; }
+    inline bool operator>=(const Iterator& other) const { return index >= other.index; }
+    inline bool operator< (const Iterator& other) const { return index <  other.index; }
+    inline bool operator> (const Iterator& other) const { return index >  other.index; }
+
+  private:
+    T value;
+    size_t index;
+  };
+
+  inline Iterator begin() const { return Iterator(value, 0); }
+  inline Iterator end() const { return Iterator(value, count); }
+
+  inline size_t size() const { return count; }
+  inline const T& operator[](ptrdiff_t) const { return value; }
+
+private:
+  T value;
+  size_t count;
+};
+
+template <typename T>
+inline constexpr Repeat<Decay<T>> repeat(T&& value, size_t count) {
+  // Returns a fake iterable which contains `count` repeats of `value`.  Useful for e.g. creating
+  // a bunch of spaces:  `kj::repeat(' ', indent * 2)`
+
+  return Repeat<Decay<T>>(value, count);
+}
+
+template <typename Inner, class Mapping>
+class MappedIterator: private Mapping {
+  // An iterator that wraps some other iterator and maps the values through a mapping function.
+  // The type `Mapping` must define a method `map()` which performs this mapping.
+
+public:
+  template <typename... Params>
+  MappedIterator(Inner inner, Params&&... params)
+      : Mapping(kj::fwd<Params>(params)...), inner(inner) {}
+
+  inline auto operator->() const { return &Mapping::map(*inner); }
+  inline decltype(auto) operator* () const { return Mapping::map(*inner); }
+  inline decltype(auto) operator[](size_t index) const { return Mapping::map(inner[index]); }
+  inline MappedIterator& operator++() { ++inner; return *this; }
+  inline MappedIterator  operator++(int) { return MappedIterator(inner++, *this); }
+  inline MappedIterator& operator--() { --inner; return *this; }
+  inline MappedIterator  operator--(int) { return MappedIterator(inner--, *this); }
+  inline MappedIterator& operator+=(ptrdiff_t amount) { inner += amount; return *this; }
+  inline MappedIterator& operator-=(ptrdiff_t amount) { inner -= amount; return *this; }
+  inline MappedIterator  operator+ (ptrdiff_t amount) const {
+    return MappedIterator(inner + amount, *this);
+  }
+  inline MappedIterator  operator- (ptrdiff_t amount) const {
+    return MappedIterator(inner - amount, *this);
+  }
+  inline ptrdiff_t operator- (const MappedIterator& other) const { return inner - other.inner; }
+
+  inline bool operator==(const MappedIterator& other) const { return inner == other.inner; }
+  inline bool operator!=(const MappedIterator& other) const { return inner != other.inner; }
+  inline bool operator<=(const MappedIterator& other) const { return inner <= other.inner; }
+  inline bool operator>=(const MappedIterator& other) const { return inner >= other.inner; }
+  inline bool operator< (const MappedIterator& other) const { return inner <  other.inner; }
+  inline bool operator> (const MappedIterator& other) const { return inner >  other.inner; }
+
+private:
+  Inner inner;
+};
+
+template <typename Inner, typename Mapping>
+class MappedIterable: private Mapping {
+  // An iterable that wraps some other iterable and maps the values through a mapping function.
+  // The type `Mapping` must define a method `map()` which performs this mapping.
+
+public:
+  template <typename... Params>
+  MappedIterable(Inner inner, Params&&... params)
+      : Mapping(kj::fwd<Params>(params)...), inner(inner) {}
+
+  typedef Decay<decltype(instance<Inner>().begin())> InnerIterator;
+  typedef MappedIterator<InnerIterator, Mapping> Iterator;
+  typedef Decay<decltype(instance<const Inner>().begin())> InnerConstIterator;
+  typedef MappedIterator<InnerConstIterator, Mapping> ConstIterator;
+
+  inline Iterator begin() { return { inner.begin(), (Mapping&)*this }; }
+  inline Iterator end() { return { inner.end(), (Mapping&)*this }; }
+  inline ConstIterator begin() const { return { inner.begin(), (const Mapping&)*this }; }
+  inline ConstIterator end() const { return { inner.end(), (const Mapping&)*this }; }
+
+private:
+  Inner inner;
+};
+
+// =======================================================================================
+// Manually invoking constructors and destructors
+//
+// ctor(x, ...) and dtor(x) invoke x's constructor or destructor, respectively.
+
+// We want placement new, but we don't want to #include <new>.  operator new cannot be defined in
+// a namespace, and defining it globally conflicts with the definition in <new>.  So we have to
+// define a dummy type and an operator new that uses it.
+
+namespace _ {  // private
+struct PlacementNew {};
+}  // namespace _ (private)
+} // namespace kj
+
+inline void* operator new(size_t, kj::_::PlacementNew, void* __p) noexcept {
+  return __p;
+}
+
+inline void operator delete(void*, kj::_::PlacementNew, void* __p) noexcept {}
+
+namespace kj {
+
+template <typename T, typename... Params>
+inline void ctor(T& location, Params&&... params) {
+  new (_::PlacementNew(), &location) T(kj::fwd<Params>(params)...);
+}
+
+template <typename T>
+inline void dtor(T& location) {
+  location.~T();
+}
+
+// =======================================================================================
+// Maybe
+//
+// Use in cases where you want to indicate that a value may be null.  Using Maybe<T&> instead of T*
+// forces the caller to handle the null case in order to satisfy the compiler, thus reliably
+// preventing null pointer dereferences at runtime.
+//
+// Maybe<T> can be implicitly constructed from T and from nullptr.
+// To read the value of a Maybe<T>, do:
+//
+//    KJ_IF_MAYBE(value, someFuncReturningMaybe()) {
+//      doSomething(*value);
+//    } else {
+//      maybeWasNull();
+//    }
+//
+// KJ_IF_MAYBE's first parameter is a variable name which will be defined within the following
+// block.  The variable will behave like a (guaranteed non-null) pointer to the Maybe's value,
+// though it may or may not actually be a pointer.
+//
+// Note that Maybe<T&> actually just wraps a pointer, whereas Maybe<T> wraps a T and a boolean
+// indicating nullness.
+
+template <typename T>
+class Maybe;
+
+namespace _ {  // private
+
+template <typename T>
+class NullableValue {
+  // Class whose interface behaves much like T*, but actually contains an instance of T and a
+  // boolean flag indicating nullness.
+
+public:
+  inline NullableValue(NullableValue&& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, kj::mv(other.value));
+    }
+  }
+  inline NullableValue(const NullableValue& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, other.value);
+    }
+  }
+  inline NullableValue(NullableValue& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, other.value);
+    }
+  }
+  inline ~NullableValue()
+#if _MSC_VER && !defined(__clang__)
+      // TODO(msvc): MSVC has a hard time with noexcept specifier expressions that are more complex
+      //   than `true` or `false`. We had a workaround for VS2015, but VS2017 regressed.
+      noexcept(false)
+#else
+      noexcept(noexcept(instance<T&>().~T()))
+#endif
+  {
+    if (isSet) {
+      dtor(value);
+    }
+  }
+
+  inline T& operator*() & { return value; }
+  inline const T& operator*() const & { return value; }
+  inline T&& operator*() && { return kj::mv(value); }
+  inline const T&& operator*() const && { return kj::mv(value); }
+  inline T* operator->() { return &value; }
+  inline const T* operator->() const { return &value; }
+  inline operator T*() { return isSet ? &value : nullptr; }
+  inline operator const T*() const { return isSet ? &value : nullptr; }
+
+  template <typename... Params>
+  inline T& emplace(Params&&... params) {
+    if (isSet) {
+      isSet = false;
+      dtor(value);
+    }
+    ctor(value, kj::fwd<Params>(params)...);
+    isSet = true;
+    return value;
+  }
+
+  inline NullableValue(): isSet(false) {}
+  inline NullableValue(T&& t)
+      : isSet(true) {
+    ctor(value, kj::mv(t));
+  }
+  inline NullableValue(T& t)
+      : isSet(true) {
+    ctor(value, t);
+  }
+  inline NullableValue(const T& t)
+      : isSet(true) {
+    ctor(value, t);
+  }
+  template <typename U>
+  inline NullableValue(NullableValue<U>&& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, kj::mv(other.value));
+    }
+  }
+  template <typename U>
+  inline NullableValue(const NullableValue<U>& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, other.value);
+    }
+  }
+  template <typename U>
+  inline NullableValue(const NullableValue<U&>& other)
+      : isSet(other.isSet) {
+    if (isSet) {
+      ctor(value, *other.ptr);
+    }
+  }
+  inline NullableValue(decltype(nullptr)): isSet(false) {}
+
+  inline NullableValue& operator=(NullableValue&& other) {
+    if (&other != this) {
+      // Careful about throwing destructors/constructors here.
+      if (isSet) {
+        isSet = false;
+        dtor(value);
+      }
+      if (other.isSet) {
+        ctor(value, kj::mv(other.value));
+        isSet = true;
+      }
+    }
+    return *this;
+  }
+
+  inline NullableValue& operator=(NullableValue& other) {
+    if (&other != this) {
+      // Careful about throwing destructors/constructors here.
+      if (isSet) {
+        isSet = false;
+        dtor(value);
+      }
+      if (other.isSet) {
+        ctor(value, other.value);
+        isSet = true;
+      }
+    }
+    return *this;
+  }
+
+  inline NullableValue& operator=(const NullableValue& other) {
+    if (&other != this) {
+      // Careful about throwing destructors/constructors here.
+      if (isSet) {
+        isSet = false;
+        dtor(value);
+      }
+      if (other.isSet) {
+        ctor(value, other.value);
+        isSet = true;
+      }
+    }
+    return *this;
+  }
+
+  inline NullableValue& operator=(T&& other) { emplace(kj::mv(other)); return *this; }
+  inline NullableValue& operator=(T& other) { emplace(other); return *this; }
+  inline NullableValue& operator=(const T& other) { emplace(other); return *this; }
+  template <typename U>
+  inline NullableValue& operator=(NullableValue<U>&& other) {
+    if (other.isSet) {
+      emplace(kj::mv(other.value));
+    } else {
+      *this = nullptr;
+    }
+    return *this;
+  }
+  template <typename U>
+  inline NullableValue& operator=(const NullableValue<U>& other) {
+    if (other.isSet) {
+      emplace(other.value);
+    } else {
+      *this = nullptr;
+    }
+    return *this;
+  }
+  template <typename U>
+  inline NullableValue& operator=(const NullableValue<U&>& other) {
+    if (other.isSet) {
+      emplace(other.value);
+    } else {
+      *this = nullptr;
+    }
+    return *this;
+  }
+  inline NullableValue& operator=(decltype(nullptr)) {
+    if (isSet) {
+      isSet = false;
+      dtor(value);
+    }
+    return *this;
+  }
+
+  inline bool operator==(decltype(nullptr)) const { return !isSet; }
+  inline bool operator!=(decltype(nullptr)) const { return isSet; }
+
+  NullableValue(const T* t) = delete;
+  NullableValue& operator=(const T* other) = delete;
+  // We used to permit assigning a Maybe<T> directly from a T*, and the assignment would check for
+  // nullness. This turned out never to be useful, and sometimes to be dangerous.
+
+private:
+  bool isSet;
+
+#if _MSC_VER && !defined(__clang__)
+#pragma warning(push)
+#pragma warning(disable: 4624)
+// Warns that the anonymous union has a deleted destructor when T is non-trivial. This warning
+// seems broken.
+#endif
+
+  union {
+    T value;
+  };
+
+#if _MSC_VER && !defined(__clang__)
+#pragma warning(pop)
+#endif
+
+  friend class kj::Maybe<T>;
+  template <typename U>
+  friend NullableValue<U>&& readMaybe(Maybe<U>&& maybe);
+};
+
+template <typename T>
+inline NullableValue<T>&& readMaybe(Maybe<T>&& maybe) { return kj::mv(maybe.ptr); }
+template <typename T>
+inline T* readMaybe(Maybe<T>& maybe) { return maybe.ptr; }
+template <typename T>
+inline const T* readMaybe(const Maybe<T>& maybe) { return maybe.ptr; }
+template <typename T>
+inline T* readMaybe(Maybe<T&>&& maybe) { return maybe.ptr; }
+template <typename T>
+inline T* readMaybe(const Maybe<T&>& maybe) { return maybe.ptr; }
+
+template <typename T>
+inline T* readMaybe(T* ptr) { return ptr; }
+// Allow KJ_IF_MAYBE to work on regular pointers.
+
+}  // namespace _ (private)
+
+#define KJ_IF_MAYBE(name, exp) if (auto name = ::kj::_::readMaybe(exp))
+
+#if __GNUC__ || __clang__
+// These two macros provide a friendly syntax to extract the value of a Maybe or return early.
+//
+// Use KJ_UNWRAP_OR_RETURN if you just want to return a simple value when the Maybe is null:
+//
+//     int foo(Maybe<int> maybe) {
+//       int value = KJ_UNWRAP_OR_RETURN(maybe, -1);
+//       // ... use value ...
+//     }
+//
+// For functions returning void, omit the second parameter to KJ_UNWRAP_OR_RETURN:
+//
+//     void foo(Maybe<int> maybe) {
+//       int value = KJ_UNWRAP_OR_RETURN(maybe);
+//       // ... use value ...
+//     }
+//
+// Use KJ_UNWRAP_OR if you want to execute a block with multiple statements.
+//
+//     int foo(Maybe<int> maybe) {
+//       int value = KJ_UNWRAP_OR(maybe, {
+//         KJ_LOG(ERROR, "problem!!!");
+//         return -1;
+//       });
+//       // ... use value ...
+//     }
+//
+// The block MUST return at the end or you will get a compiler error
+//
+// Unfortunately, these macros seem impossible to express without using GCC's non-standard
+// "statement expressions" extension. IIFEs don't do the trick here because a lambda cannot
+// return out of the parent scope. These macros should therefore only be used in projects that
+// target GCC or GCC-compatible compilers.
+//
+// `__GNUC__` is not defined when using LLVM's MSVC-compatible compiler driver `clang-cl` (even
+// though clang supports the required extension), hence the additional `|| __clang__`.
+
+#define KJ_UNWRAP_OR_RETURN(value, ...) \
+  (*({ \
+    auto _kj_result = ::kj::_::readMaybe(value); \
+    if (!_kj_result) { \
+      return __VA_ARGS__; \
+    } \
+    kj::mv(_kj_result); \
+  }))
+
+#define KJ_UNWRAP_OR(value, block) \
+  (*({ \
+    auto _kj_result = ::kj::_::readMaybe(value); \
+    if (!_kj_result) { \
+      block; \
+      asm("KJ_UNWRAP_OR_block_is_missing_return_statement\n"); \
+    } \
+    kj::mv(_kj_result); \
+  }))
+#endif
+
+template <typename T>
+class Maybe {
+  // A T, or nullptr.
+
+  // IF YOU CHANGE THIS CLASS:  Note that there is a specialization of it in memory.h.
+
+public:
+  Maybe(): ptr(nullptr) {}
+  Maybe(T&& t): ptr(kj::mv(t)) {}
+  Maybe(T& t): ptr(t) {}
+  Maybe(const T& t): ptr(t) {}
+  Maybe(Maybe&& other): ptr(kj::mv(other.ptr)) { other = nullptr; }
+  Maybe(const Maybe& other): ptr(other.ptr) {}
+  Maybe(Maybe& other): ptr(other.ptr) {}
+
+  template <typename U>
+  Maybe(Maybe<U>&& other) {
+    KJ_IF_MAYBE(val, kj::mv(other)) {
+      ptr.emplace(kj::mv(*val));
+      other = nullptr;
+    }
+  }
+  template <typename U>
+  Maybe(Maybe<U&>&& other) {
+    KJ_IF_MAYBE(val, other) {
+      ptr.emplace(*val);
+      other = nullptr;
+    }
+  }
+  template <typename U>
+  Maybe(const Maybe<U>& other) {
+    KJ_IF_MAYBE(val, other) {
+      ptr.emplace(*val);
+    }
+  }
+
+  Maybe(decltype(nullptr)): ptr(nullptr) {}
+
+  template <typename... Params>
+  inline T& emplace(Params&&... params) {
+    // Replace this Maybe's content with a new value constructed by passing the given parameters to
+    // T's constructor. This can be used to initialize a Maybe without copying or even moving a T.
+    // Returns a reference to the newly-constructed value.
+
+    return ptr.emplace(kj::fwd<Params>(params)...);
+  }
+
+  inline Maybe& operator=(T&& other) { ptr = kj::mv(other); return *this; }
+  inline Maybe& operator=(T& other) { ptr = other; return *this; }
+  inline Maybe& operator=(const T& other) { ptr = other; return *this; }
+
+  inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); other = nullptr; return *this; }
+  inline Maybe& operator=(Maybe& other) { ptr = other.ptr; return *this; }
+  inline Maybe& operator=(const Maybe& other) { ptr = other.ptr; return *this; }
+
+  template <typename U>
+  Maybe& operator=(Maybe<U>&& other) {
+    KJ_IF_MAYBE(val, kj::mv(other)) {
+      ptr.emplace(kj::mv(*val));
+      other = nullptr;
+    } else {
+      ptr = nullptr;
+    }
+    return *this;
+  }
+  template <typename U>
+  Maybe& operator=(const Maybe<U>& other) {
+    KJ_IF_MAYBE(val, other) {
+      ptr.emplace(*val);
+    } else {
+      ptr = nullptr;
+    }
+    return *this;
+  }
+
+  inline Maybe& operator=(decltype(nullptr)) { ptr = nullptr; return *this; }
+
+  inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
+  inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
+
+  inline bool operator==(const Maybe<T>& other) const {
+    if (ptr == nullptr) {
+      return other == nullptr;
+    } else {
+      return other.ptr != nullptr && *ptr == *other.ptr;
+    }
+  }
+  inline bool operator!=(const Maybe<T>& other) const { return !(*this == other); }
+
+  Maybe(const T* t) = delete;
+  Maybe& operator=(const T* other) = delete;
+  // We used to permit assigning a Maybe<T> directly from a T*, and the assignment would check for
+  // nullness. This turned out never to be useful, and sometimes to be dangerous.
+
+  T& orDefault(T& defaultValue) & {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return *ptr;
+    }
+  }
+  const T& orDefault(const T& defaultValue) const & {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return *ptr;
+    }
+  }
+  T&& orDefault(T&& defaultValue) && {
+    if (ptr == nullptr) {
+      return kj::mv(defaultValue);
+    } else {
+      return kj::mv(*ptr);
+    }
+  }
+  const T&& orDefault(const T&& defaultValue) const && {
+    if (ptr == nullptr) {
+      return kj::mv(defaultValue);
+    } else {
+      return kj::mv(*ptr);
+    }
+  }
+
+  template <typename F,
+      typename Result = decltype(instance<bool>() ? instance<T&>() : instance<F>()())>
+  Result orDefault(F&& lazyDefaultValue) & {
+    if (ptr == nullptr) {
+      return lazyDefaultValue();
+    } else {
+      return *ptr;
+    }
+  }
+
+  template <typename F,
+      typename Result = decltype(instance<bool>() ? instance<const T&>() : instance<F>()())>
+  Result orDefault(F&& lazyDefaultValue) const & {
+    if (ptr == nullptr) {
+      return lazyDefaultValue();
+    } else {
+      return *ptr;
+    }
+  }
+
+  template <typename F,
+      typename Result = decltype(instance<bool>() ? instance<T&&>() : instance<F>()())>
+  Result orDefault(F&& lazyDefaultValue) && {
+    if (ptr == nullptr) {
+      return lazyDefaultValue();
+    } else {
+      return kj::mv(*ptr);
+    }
+  }
+
+  template <typename F,
+      typename Result = decltype(instance<bool>() ? instance<const T&&>() : instance<F>()())>
+  Result orDefault(F&& lazyDefaultValue) const && {
+    if (ptr == nullptr) {
+      return lazyDefaultValue();
+    } else {
+      return kj::mv(*ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) & -> Maybe<decltype(f(instance<T&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(*ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) const & -> Maybe<decltype(f(instance<const T&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(*ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) && -> Maybe<decltype(f(instance<T&&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(kj::mv(*ptr));
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) const && -> Maybe<decltype(f(instance<const T&&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(kj::mv(*ptr));
+    }
+  }
+
+private:
+  _::NullableValue<T> ptr;
+
+  template <typename U>
+  friend class Maybe;
+  template <typename U>
+  friend _::NullableValue<U>&& _::readMaybe(Maybe<U>&& maybe);
+  template <typename U>
+  friend U* _::readMaybe(Maybe<U>& maybe);
+  template <typename U>
+  friend const U* _::readMaybe(const Maybe<U>& maybe);
+};
+
+template <typename T>
+class Maybe<T&> {
+public:
+  constexpr Maybe(): ptr(nullptr) {}
+  constexpr Maybe(T& t): ptr(&t) {}
+  constexpr Maybe(T* t): ptr(t) {}
+
+  inline constexpr Maybe(PropagateConst<T, Maybe>& other): ptr(other.ptr) {}
+  // Allow const copy only if `T` itself is const. Otherwise allow only non-const copy, to
+  // protect transitive constness. Clang is happy for this constructor to be declared `= default`
+  // since, after evaluation of `PropagateConst`, it does end up being a default-able constructor.
+  // But, GCC and MSVC both complain about that, claiming this constructor cannot be declared
+  // default. I don't know who is correct, but whatever, we'll write out an implementation, fine.
+  //
+  // Note that we can't solve this by inheriting DisallowConstCopyIfNotConst<T> because we want
+  // to override the move constructor, and if we override the move constructor then we must define
+  // the copy constructor here.
+
+  inline constexpr Maybe(Maybe&& other): ptr(other.ptr) { other.ptr = nullptr; }
+
+  template <typename U>
+  inline constexpr Maybe(Maybe<U&>& other): ptr(other.ptr) {}
+  template <typename U>
+  inline constexpr Maybe(const Maybe<U&>& other): ptr(const_cast<const U*>(other.ptr)) {}
+  template <typename U>
+  inline constexpr Maybe(Maybe<U&>&& other): ptr(other.ptr) { other.ptr = nullptr; }
+  template <typename U>
+  inline constexpr Maybe(const Maybe<U&>&& other) = delete;
+  template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
+  constexpr Maybe(Maybe<U>& other): ptr(other.ptr.operator U*()) {}
+  template <typename U, typename = EnableIf<canConvert<const U*, T*>()>>
+  constexpr Maybe(const Maybe<U>& other): ptr(other.ptr.operator const U*()) {}
+  inline constexpr Maybe(decltype(nullptr)): ptr(nullptr) {}
+
+  inline Maybe& operator=(T& other) { ptr = &other; return *this; }
+  inline Maybe& operator=(T* other) { ptr = other; return *this; }
+  inline Maybe& operator=(PropagateConst<T, Maybe>& other) { ptr = other.ptr; return *this; }
+  inline Maybe& operator=(Maybe&& other) { ptr = other.ptr; other.ptr = nullptr; return *this; }
+  template <typename U>
+  inline Maybe& operator=(Maybe<U&>& other) { ptr = other.ptr; return *this; }
+  template <typename U>
+  inline Maybe& operator=(const Maybe<const U&>& other) { ptr = other.ptr; return *this; }
+  template <typename U>
+  inline Maybe& operator=(Maybe<U&>&& other) { ptr = other.ptr; other.ptr = nullptr; return *this; }
+  template <typename U>
+  inline Maybe& operator=(const Maybe<U&>&& other) = delete;
+
+  inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
+  inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
+
+  T& orDefault(T& defaultValue) {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return *ptr;
+    }
+  }
+  const T& orDefault(const T& defaultValue) const {
+    if (ptr == nullptr) {
+      return defaultValue;
+    } else {
+      return *ptr;
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) -> Maybe<decltype(f(instance<T&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      return f(*ptr);
+    }
+  }
+
+  template <typename Func>
+  auto map(Func&& f) const -> Maybe<decltype(f(instance<const T&>()))> {
+    if (ptr == nullptr) {
+      return nullptr;
+    } else {
+      const T& ref = *ptr;
+      return f(ref);
+    }
+  }
+
+private:
+  T* ptr;
+
+  template <typename U>
+  friend class Maybe;
+  template <typename U>
+  friend U* _::readMaybe(Maybe<U&>&& maybe);
+  template <typename U>
+  friend U* _::readMaybe(const Maybe<U&>& maybe);
+};
+
+// =======================================================================================
+// ArrayPtr
+//
+// So common that we put it in common.h rather than array.h.
+
+template <typename T>
+class Array;
+
+template <typename T>
+class ArrayPtr: public DisallowConstCopyIfNotConst<T> {
+  // A pointer to an array.  Includes a size.  Like any pointer, it doesn't own the target data,
+  // and passing by value only copies the pointer, not the target.
+
+public:
+  inline constexpr ArrayPtr(): ptr(nullptr), size_(0) {}
+  inline constexpr ArrayPtr(decltype(nullptr)): ptr(nullptr), size_(0) {}
+  inline constexpr ArrayPtr(T* ptr KJ_LIFETIMEBOUND, size_t size): ptr(ptr), size_(size) {}
+  inline constexpr ArrayPtr(T* begin KJ_LIFETIMEBOUND, T* end KJ_LIFETIMEBOUND)
+      : ptr(begin), size_(end - begin) {}
+  ArrayPtr<T>& operator=(Array<T>&&) = delete;
+  ArrayPtr<T>& operator=(decltype(nullptr)) {
+    ptr = nullptr;
+    size_ = 0;
+    return *this;
+  }
+
+#if __GNUC__ && !__clang__ && __GNUC__ >= 9
+// GCC 9 added a warning when we take an initializer_list as a constructor parameter and save a
+// pointer to its content in a class member. GCC apparently imagines we're going to do something
+// dumb like this:
+//     ArrayPtr<const int> ptr = { 1, 2, 3 };
+//     foo(ptr[1]); // undefined behavior!
+// Any KJ programmer should be able to recognize that this is UB, because an ArrayPtr does not own
+// its content. That's not what this constructor is for, tohugh. This constructor is meant to allow
+// code like this:
+//     int foo(ArrayPtr<const int> p);
+//     // ... later ...
+//     foo({1, 2, 3});
+// In this case, the initializer_list's backing array, like any temporary, lives until the end of
+// the statement `foo({1, 2, 3});`. Therefore, it lives at least until the call to foo() has
+// returned, which is exactly what we care about. This usage is fine! GCC is wrong to warn.
+//
+// Amusingly, Clang's implementation has a similar type that they call ArrayRef which apparently
+// triggers this same GCC warning. My guess is that Clang will not introduce a similar warning
+// given that it triggers on their own, legitimate code.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Winit-list-lifetime"
+#endif
+  inline KJ_CONSTEXPR() ArrayPtr(
+      ::std::initializer_list<RemoveConstOrDisable<T>> init KJ_LIFETIMEBOUND)
+      : ptr(init.begin()), size_(init.size()) {}
+#if __GNUC__ && !__clang__ && __GNUC__ >= 9
+#pragma GCC diagnostic pop
+#endif
+
+  template <size_t size>
+  inline constexpr ArrayPtr(KJ_LIFETIMEBOUND T (&native)[size]): ptr(native), size_(size) {
+    // Construct an ArrayPtr from a native C-style array.
+    //
+    // We disable this constructor for const char arrays because otherwise you would be able to
+    // implicitly convert a character literal to ArrayPtr<const char>, which sounds really great,
+    // except that the NUL terminator would be included, which probably isn't what you intended.
+    //
+    // TODO(someday): Maybe we should support character literals but explicitly chop off the NUL
+    //   terminator. This could do the wrong thing if someone tries to construct an
+    //   ArrayPtr<const char> from a non-NUL-terminated char array, but evidence suggests that all
+    //   real use cases are in fact intending to remove the NUL terminator. It's convenient to be
+    //   able to specify ArrayPtr<const char> as a parameter type and be able to accept strings
+    //   as input in addition to arrays. Currently, you'll need overloading to support string
+    //   literals in this case, but if you overload StringPtr, then you'll find that several
+    //   conversions (e.g. from String and from a literal char array) become ambiguous! You end up
+    //   having to overload for literal char arrays specifically which is cumbersome.
+
+    static_assert(!isSameType<T, const char>(),
+        "Can't implicitly convert literal char array to ArrayPtr because we don't know if "
+        "you meant to include the NUL terminator. We may change this in the future to "
+        "automatically drop the NUL terminator. For now, try explicitly converting to StringPtr, "
+        "which can in turn implicitly convert to ArrayPtr<const char>.");
+    static_assert(!isSameType<T, const char16_t>(), "see above");
+    static_assert(!isSameType<T, const char32_t>(), "see above");
+  }
+
+  inline operator ArrayPtr<const T>() const {
+    return ArrayPtr<const T>(ptr, size_);
+  }
+  inline ArrayPtr<const T> asConst() const {
+    return ArrayPtr<const T>(ptr, size_);
+  }
+
+  inline constexpr size_t size() const { return size_; }
+  inline const T& operator[](size_t index) const {
+    KJ_IREQUIRE(index < size_, "Out-of-bounds ArrayPtr access.");
+    return ptr[index];
+  }
+  inline T& operator[](size_t index) {
+    KJ_IREQUIRE(index < size_, "Out-of-bounds ArrayPtr access.");
+    return ptr[index];
+  }
+
+  inline T* begin() { return ptr; }
+  inline T* end() { return ptr + size_; }
+  inline T& front() { return *ptr; }
+  inline T& back() { return *(ptr + size_ - 1); }
+  inline constexpr const T* begin() const { return ptr; }
+  inline constexpr const T* end() const { return ptr + size_; }
+  inline const T& front() const { return *ptr; }
+  inline const T& back() const { return *(ptr + size_ - 1); }
+
+  inline ArrayPtr<const T> slice(size_t start, size_t end) const {
+    KJ_IREQUIRE(start <= end && end <= size_, "Out-of-bounds ArrayPtr::slice().");
+    return ArrayPtr<const T>(ptr + start, end - start);
+  }
+  inline ArrayPtr slice(size_t start, size_t end) {
+    KJ_IREQUIRE(start <= end && end <= size_, "Out-of-bounds ArrayPtr::slice().");
+    return ArrayPtr(ptr + start, end - start);
+  }
+  inline bool startsWith(const ArrayPtr<const T>& other) const {
+    return other.size() <= size_ && slice(0, other.size()) == other;
+  }
+  inline bool endsWith(const ArrayPtr<const T>& other) const {
+    return other.size() <= size_ && slice(size_ - other.size(), size_) == other;
+  }
+
+  inline Maybe<size_t> findFirst(const T& match) const {
+    for (size_t i = 0; i < size_; i++) {
+      if (ptr[i] == match) {
+        return i;
+      }
+    }
+    return nullptr;
+  }
+  inline Maybe<size_t> findLast(const T& match) const {
+    for (size_t i = size_; i--;) {
+      if (ptr[i] == match) {
+        return i;
+      }
+    }
+    return nullptr;
+  }
+
+  inline ArrayPtr<PropagateConst<T, byte>> asBytes() const {
+    // Reinterpret the array as a byte array. This is explicitly legal under C++ aliasing
+    // rules.
+    return { reinterpret_cast<PropagateConst<T, byte>*>(ptr), size_ * sizeof(T) };
+  }
+  inline ArrayPtr<PropagateConst<T, char>> asChars() const {
+    // Reinterpret the array as a char array. This is explicitly legal under C++ aliasing
+    // rules.
+    return { reinterpret_cast<PropagateConst<T, char>*>(ptr), size_ * sizeof(T) };
+  }
+
+  inline bool operator==(decltype(nullptr)) const { return size_ == 0; }
+  inline bool operator!=(decltype(nullptr)) const { return size_ != 0; }
+
+  inline bool operator==(const ArrayPtr& other) const {
+    if (size_ != other.size_) return false;
+    if (isIntegral<RemoveConst<T>>()) {
+      if (size_ == 0) return true;
+      return memcmp(ptr, other.ptr, size_ * sizeof(T)) == 0;
+    }
+    for (size_t i = 0; i < size_; i++) {
+      if (ptr[i] != other[i]) return false;
+    }
+    return true;
+  }
+#if !__cpp_impl_three_way_comparison
+  inline bool operator!=(const ArrayPtr& other) const { return !(*this == other); }
+#endif
+
+  template <typename U>
+  inline bool operator==(const ArrayPtr<U>& other) const {
+    if (size_ != other.size()) return false;
+    for (size_t i = 0; i < size_; i++) {
+      if (ptr[i] != other[i]) return false;
+    }
+    return true;
+  }
+#if !__cpp_impl_three_way_comparison
+  template <typename U>
+  inline bool operator!=(const ArrayPtr<U>& other) const { return !(*this == other); }
+#endif
+
+  template <typename... Attachments>
+  Array<T> attach(Attachments&&... attachments) const KJ_WARN_UNUSED_RESULT;
+  // Like Array<T>::attach(), but also promotes an ArrayPtr to an Array. Generally the attachment
+  // should be an object that actually owns the array that the ArrayPtr is pointing at.
+  //
+  // You must include kj/array.h to call this.
+
+private:
+  T* ptr;
+  size_t size_;
+};
+
+template <>
+inline Maybe<size_t> ArrayPtr<const char>::findFirst(const char& c) const {
+  const char* pos = reinterpret_cast<const char*>(memchr(ptr, c, size_));
+  if (pos == nullptr) {
+    return nullptr;
+  } else {
+    return pos - ptr;
+  }
+}
+
+template <>
+inline Maybe<size_t> ArrayPtr<char>::findFirst(const char& c) const {
+  char* pos = reinterpret_cast<char*>(memchr(ptr, c, size_));
+  if (pos == nullptr) {
+    return nullptr;
+  } else {
+    return pos - ptr;
+  }
+}
+
+template <>
+inline Maybe<size_t> ArrayPtr<const byte>::findFirst(const byte& c) const {
+  const byte* pos = reinterpret_cast<const byte*>(memchr(ptr, c, size_));
+  if (pos == nullptr) {
+    return nullptr;
+  } else {
+    return pos - ptr;
+  }
+}
+
+template <>
+inline Maybe<size_t> ArrayPtr<byte>::findFirst(const byte& c) const {
+  byte* pos = reinterpret_cast<byte*>(memchr(ptr, c, size_));
+  if (pos == nullptr) {
+    return nullptr;
+  } else {
+    return pos - ptr;
+  }
+}
+
+// glibc has a memrchr() for reverse search but it's non-standard, so we don't bother optimizing
+// findLast(), which isn't used much anyway.
+
+template <typename T>
+inline constexpr ArrayPtr<T> arrayPtr(T* ptr KJ_LIFETIMEBOUND, size_t size) {
+  // Use this function to construct ArrayPtrs without writing out the type name.
+  return ArrayPtr<T>(ptr, size);
+}
+
+template <typename T>
+inline constexpr ArrayPtr<T> arrayPtr(T* begin KJ_LIFETIMEBOUND, T* end KJ_LIFETIMEBOUND) {
+  // Use this function to construct ArrayPtrs without writing out the type name.
+  return ArrayPtr<T>(begin, end);
+}
+
+// =======================================================================================
+// Casts
+
+template <typename To, typename From>
+To implicitCast(From&& from) {
+  // `implicitCast<T>(value)` casts `value` to type `T` only if the conversion is implicit.  Useful
+  // for e.g. resolving ambiguous overloads without sacrificing type-safety.
+  return kj::fwd<From>(from);
+}
+
+template <typename To, typename From>
+Maybe<To&> dynamicDowncastIfAvailable(From& from) {
+  // If RTTI is disabled, always returns nullptr.  Otherwise, works like dynamic_cast.  Useful
+  // in situations where dynamic_cast could allow an optimization, but isn't strictly necessary
+  // for correctness.  It is highly recommended that you try to arrange all your dynamic_casts
+  // this way, as a dynamic_cast that is necessary for correctness implies a flaw in the interface
+  // design.
+
+  // Force a compile error if To is not a subtype of From.  Cross-casting is rare; if it is needed
+  // we should have a separate cast function like dynamicCrosscastIfAvailable().
+  if (false) {
+    kj::implicitCast<From*>(kj::implicitCast<To*>(nullptr));
+  }
+
+#if KJ_NO_RTTI
+  return nullptr;
+#else
+  return dynamic_cast<To*>(&from);
+#endif
+}
+
+template <typename To, typename From>
+To& downcast(From& from) {
+  // Down-cast a value to a sub-type, asserting that the cast is valid.  In opt mode this is a
+  // static_cast, but in debug mode (when RTTI is enabled) a dynamic_cast will be used to verify
+  // that the value really has the requested type.
+
+  // Force a compile error if To is not a subtype of From.
+  if (false) {
+    kj::implicitCast<From*>(kj::implicitCast<To*>(nullptr));
+  }
+
+#if !KJ_NO_RTTI
+  KJ_IREQUIRE(dynamic_cast<To*>(&from) != nullptr, "Value cannot be downcast() to requested type.");
+#endif
+
+  return static_cast<To&>(from);
+}
+
+// =======================================================================================
+// Defer
+
+namespace _ {  // private
+
+template <typename Func>
+class Deferred {
+public:
+  Deferred(Func&& func): maybeFunc(kj::fwd<Func>(func)) {}
+  ~Deferred() noexcept(false) {
+    run();
+  }
+  KJ_DISALLOW_COPY(Deferred);
+
+  Deferred(Deferred&&) = default;
+  // Since we use a kj::Maybe, the default move constructor does exactly what we want it to do.
+
+  void run() {
+    // Move `maybeFunc` to the local scope so that even if we throw, we destroy the functor we had.
+    auto maybeLocalFunc = kj::mv(maybeFunc);
+    KJ_IF_MAYBE(func, maybeLocalFunc) {
+      (*func)();
+    }
+  }
+
+  void cancel() {
+    maybeFunc = nullptr;
+  }
+
+private:
+  kj::Maybe<Func> maybeFunc;
+  // Note that `Func` may actually be an lvalue reference because `kj::defer` takes its argument via
+  // universal reference. `kj::Maybe` has specializations for lvalue reference types, so this works
+  // out.
+};
+
+}  // namespace _ (private)
+
+template <typename Func>
+_::Deferred<Func> defer(Func&& func) {
+  // Returns an object which will invoke the given functor in its destructor. The object is not
+  // copyable but is move-constructable with the semantics you'd expect. Since the return type is
+  // private, you need to assign to an `auto` variable.
+  //
+  // The KJ_DEFER macro provides slightly more convenient syntax for the common case where you
+  // want some code to run at current scope exit.
+  //
+  // KJ_DEFER does not support move-assignment for its returned objects. If you need to reuse the
+  // variable for your deferred function object, then you will want to write your own class for that
+  // purpose.
+
+  return _::Deferred<Func>(kj::fwd<Func>(func));
+}
+
+#define KJ_DEFER(code) auto KJ_UNIQUE_NAME(_kjDefer) = ::kj::defer([&](){code;})
+// Run the given code when the function exits, whether by return or exception.
+
+}  // namespace kj
+
+KJ_END_HEADER