jpayne@69: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
jpayne@69: // Licensed under the MIT License:
jpayne@69: //
jpayne@69: // Permission is hereby granted, free of charge, to any person obtaining a copy
jpayne@69: // of this software and associated documentation files (the "Software"), to deal
jpayne@69: // in the Software without restriction, including without limitation the rights
jpayne@69: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
jpayne@69: // copies of the Software, and to permit persons to whom the Software is
jpayne@69: // furnished to do so, subject to the following conditions:
jpayne@69: //
jpayne@69: // The above copyright notice and this permission notice shall be included in
jpayne@69: // all copies or substantial portions of the Software.
jpayne@69: //
jpayne@69: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
jpayne@69: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
jpayne@69: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
jpayne@69: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
jpayne@69: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
jpayne@69: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
jpayne@69: // THE SOFTWARE.
jpayne@69: 
jpayne@69: // This file defines a notion of tuples that is simpler than `std::tuple`.  It works as follows:
jpayne@69: // - `kj::Tuple<A, B, C> is the type of a tuple of an A, a B, and a C.
jpayne@69: // - `kj::tuple(a, b, c)` returns a tuple containing a, b, and c.  If any of these are themselves
jpayne@69: //   tuples, they are flattened, so `tuple(a, tuple(b, c), d)` is equivalent to `tuple(a, b, c, d)`.
jpayne@69: // - `kj::get<n>(myTuple)` returns the element of `myTuple` at index n.
jpayne@69: // - `kj::apply(func, ...)` calls func on the following arguments after first expanding any tuples
jpayne@69: //   in the argument list.  So `kj::apply(foo, a, tuple(b, c), d)` would call `foo(a, b, c, d)`.
jpayne@69: //
jpayne@69: // Note that:
jpayne@69: // - The type `Tuple<T>` is a synonym for T.  This is why `get` and `apply` are not members of the
jpayne@69: //   type.
jpayne@69: // - It is illegal for an element of `Tuple` to itself be a tuple, as tuples are meant to be
jpayne@69: //   flattened.
jpayne@69: // - It is illegal for an element of `Tuple` to be a reference, due to problems this would cause
jpayne@69: //   with type inference and `tuple()`.
jpayne@69: 
jpayne@69: #pragma once
jpayne@69: 
jpayne@69: #include "common.h"
jpayne@69: 
jpayne@69: KJ_BEGIN_HEADER
jpayne@69: 
jpayne@69: namespace kj {
jpayne@69: namespace _ {  // private
jpayne@69: 
jpayne@69: template <size_t index, typename... T>
jpayne@69: struct TypeByIndex_;
jpayne@69: template <typename First, typename... Rest>
jpayne@69: struct TypeByIndex_<0, First, Rest...> {
jpayne@69:   typedef First Type;
jpayne@69: };
jpayne@69: template <size_t index, typename First, typename... Rest>
jpayne@69: struct TypeByIndex_<index, First, Rest...>
jpayne@69:     : public TypeByIndex_<index - 1, Rest...> {};
jpayne@69: template <size_t index>
jpayne@69: struct TypeByIndex_<index> {
jpayne@69:   static_assert(index != index, "Index out-of-range.");
jpayne@69: };
jpayne@69: template <size_t index, typename... T>
jpayne@69: using TypeByIndex = typename TypeByIndex_<index, T...>::Type;
jpayne@69: // Chose a particular type out of a list of types, by index.
jpayne@69: 
jpayne@69: template <size_t... s>
jpayne@69: struct Indexes {};
jpayne@69: // Dummy helper type that just encapsulates a sequential list of indexes, so that we can match
jpayne@69: // templates against them and unpack them with '...'.
jpayne@69: 
jpayne@69: template <size_t end, size_t... prefix>
jpayne@69: struct MakeIndexes_: public MakeIndexes_<end - 1, end - 1, prefix...> {};
jpayne@69: template <size_t... prefix>
jpayne@69: struct MakeIndexes_<0, prefix...> {
jpayne@69:   typedef Indexes<prefix...> Type;
jpayne@69: };
jpayne@69: template <size_t end>
jpayne@69: using MakeIndexes = typename MakeIndexes_<end>::Type;
jpayne@69: // Equivalent to Indexes<0, 1, 2, ..., end>.
jpayne@69: 
jpayne@69: template <typename... T>
jpayne@69: class Tuple;
jpayne@69: template <size_t index, typename... U>
jpayne@69: inline TypeByIndex<index, U...>& getImpl(Tuple<U...>& tuple);
jpayne@69: template <size_t index, typename... U>
jpayne@69: inline TypeByIndex<index, U...>&& getImpl(Tuple<U...>&& tuple);
jpayne@69: template <size_t index, typename... U>
jpayne@69: inline const TypeByIndex<index, U...>& getImpl(const Tuple<U...>& tuple);
jpayne@69: 
jpayne@69: template <uint index, typename T>
jpayne@69: struct TupleElement {
jpayne@69:   // Encapsulates one element of a tuple.  The actual tuple implementation multiply-inherits
jpayne@69:   // from a TupleElement for each element, which is more efficient than a recursive definition.
jpayne@69: 
jpayne@69:   T value;
jpayne@69:   TupleElement() = default;
jpayne@69:   constexpr inline TupleElement(const T& value): value(value) {}
jpayne@69:   constexpr inline TupleElement(T&& value): value(kj::mv(value)) {}
jpayne@69: };
jpayne@69: 
jpayne@69: template <uint index, typename T>
jpayne@69: struct TupleElement<index, T&> {
jpayne@69:   // A tuple containing references can be constructed using refTuple().
jpayne@69: 
jpayne@69:   T& value;
jpayne@69:   constexpr inline TupleElement(T& value): value(value) {}
jpayne@69: };
jpayne@69: 
jpayne@69: template <uint index, typename... T>
jpayne@69: struct TupleElement<index, Tuple<T...>> {
jpayne@69:   static_assert(sizeof(Tuple<T...>*) == 0,
jpayne@69:                 "Tuples cannot contain other tuples -- they should be flattened.");
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename Indexes, typename... Types>
jpayne@69: struct TupleImpl;
jpayne@69: 
jpayne@69: template <size_t... indexes, typename... Types>
jpayne@69: struct TupleImpl<Indexes<indexes...>, Types...>
jpayne@69:     : public TupleElement<indexes, Types>... {
jpayne@69:   // Implementation of Tuple.  The only reason we need this rather than rolling this into class
jpayne@69:   // Tuple (below) is so that we can get "indexes" as an unpackable list.
jpayne@69: 
jpayne@69:   static_assert(sizeof...(indexes) == sizeof...(Types), "Incorrect use of TupleImpl.");
jpayne@69: 
jpayne@69:   TupleImpl() = default;
jpayne@69: 
jpayne@69:   template <typename... Params>
jpayne@69:   inline TupleImpl(Params&&... params)
jpayne@69:       : TupleElement<indexes, Types>(kj::fwd<Params>(params))... {
jpayne@69:     // Work around Clang 3.2 bug 16303 where this is not detected.  (Unfortunately, Clang sometimes
jpayne@69:     // segfaults instead.)
jpayne@69:     static_assert(sizeof...(params) == sizeof...(indexes),
jpayne@69:                   "Wrong number of parameters to Tuple constructor.");
jpayne@69:   }
jpayne@69: 
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline TupleImpl(Tuple<U...>&& other)
jpayne@69:       : TupleElement<indexes, Types>(kj::fwd<U>(getImpl<indexes>(other)))... {}
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline TupleImpl(Tuple<U...>& other)
jpayne@69:       : TupleElement<indexes, Types>(getImpl<indexes>(other))... {}
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline TupleImpl(const Tuple<U...>& other)
jpayne@69:       : TupleElement<indexes, Types>(getImpl<indexes>(other))... {}
jpayne@69: };
jpayne@69: 
jpayne@69: struct MakeTupleFunc;
jpayne@69: struct MakeRefTupleFunc;
jpayne@69: 
jpayne@69: template <typename... T>
jpayne@69: class Tuple {
jpayne@69:   // The actual Tuple class (used for tuples of size other than 1).
jpayne@69: 
jpayne@69: public:
jpayne@69:   Tuple() = default;
jpayne@69: 
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline Tuple(Tuple<U...>&& other): impl(kj::mv(other)) {}
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline Tuple(Tuple<U...>& other): impl(other) {}
jpayne@69:   template <typename... U>
jpayne@69:   constexpr inline Tuple(const Tuple<U...>& other): impl(other) {}
jpayne@69: 
jpayne@69: private:
jpayne@69:   template <typename... Params>
jpayne@69:   constexpr Tuple(Params&&... params): impl(kj::fwd<Params>(params)...) {}
jpayne@69: 
jpayne@69:   TupleImpl<MakeIndexes<sizeof...(T)>, T...> impl;
jpayne@69: 
jpayne@69:   template <size_t index, typename... U>
jpayne@69:   friend inline TypeByIndex<index, U...>& getImpl(Tuple<U...>& tuple);
jpayne@69:   template <size_t index, typename... U>
jpayne@69:   friend inline TypeByIndex<index, U...>&& getImpl(Tuple<U...>&& tuple);
jpayne@69:   template <size_t index, typename... U>
jpayne@69:   friend inline const TypeByIndex<index, U...>& getImpl(const Tuple<U...>& tuple);
jpayne@69:   friend struct MakeTupleFunc;
jpayne@69:   friend struct MakeRefTupleFunc;
jpayne@69: };
jpayne@69: 
jpayne@69: template <>
jpayne@69: class Tuple<> {
jpayne@69:   // Simplified zero-member version of Tuple.  In particular this is important to make sure that
jpayne@69:   // Tuple<>() is constexpr.
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: class Tuple<T>;
jpayne@69: // Single-element tuple should never be used.  The public API should ensure this.
jpayne@69: 
jpayne@69: template <size_t index, typename... T>
jpayne@69: inline TypeByIndex<index, T...>& getImpl(Tuple<T...>& tuple) {
jpayne@69:   // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
jpayne@69:   static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
jpayne@69:   return implicitCast<TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value;
jpayne@69: }
jpayne@69: template <size_t index, typename... T>
jpayne@69: inline TypeByIndex<index, T...>&& getImpl(Tuple<T...>&& tuple) {
jpayne@69:   // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
jpayne@69:   static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
jpayne@69:   return kj::mv(implicitCast<TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value);
jpayne@69: }
jpayne@69: template <size_t index, typename... T>
jpayne@69: inline const TypeByIndex<index, T...>& getImpl(const Tuple<T...>& tuple) {
jpayne@69:   // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
jpayne@69:   static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
jpayne@69:   return implicitCast<const TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value;
jpayne@69: }
jpayne@69: template <size_t index, typename T>
jpayne@69: inline T&& getImpl(T&& value) {
jpayne@69:   // Get member of a Tuple by index, e.g. `getImpl<2>(myTuple)`.
jpayne@69: 
jpayne@69:   // Non-tuples are equivalent to one-element tuples.
jpayne@69:   static_assert(index == 0, "Tuple element index out-of-bounds.");
jpayne@69:   return kj::fwd<T>(value);
jpayne@69: }
jpayne@69: 
jpayne@69: 
jpayne@69: template <typename Func, typename SoFar, typename... T>
jpayne@69: struct ExpandAndApplyResult_;
jpayne@69: // Template which computes the return type of applying Func to T... after flattening tuples.
jpayne@69: // SoFar starts as Tuple<> and accumulates the flattened parameter types -- so after this template
jpayne@69: // is recursively expanded, T... is empty and SoFar is a Tuple containing all the parameters.
jpayne@69: 
jpayne@69: template <typename Func, typename First, typename... Rest, typename... T>
jpayne@69: struct ExpandAndApplyResult_<Func, Tuple<T...>, First, Rest...>
jpayne@69:     : public ExpandAndApplyResult_<Func, Tuple<T..., First>, Rest...> {};
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
jpayne@69: struct ExpandAndApplyResult_<Func, Tuple<T...>, Tuple<FirstTypes...>, Rest...>
jpayne@69:     : public ExpandAndApplyResult_<Func, Tuple<T...>, FirstTypes&&..., Rest...> {};
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
jpayne@69: struct ExpandAndApplyResult_<Func, Tuple<T...>, Tuple<FirstTypes...>&, Rest...>
jpayne@69:     : public ExpandAndApplyResult_<Func, Tuple<T...>, FirstTypes&..., Rest...> {};
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
jpayne@69: struct ExpandAndApplyResult_<Func, Tuple<T...>, const Tuple<FirstTypes...>&, Rest...>
jpayne@69:     : public ExpandAndApplyResult_<Func, Tuple<T...>, const FirstTypes&..., Rest...> {};
jpayne@69: template <typename Func, typename... T>
jpayne@69: struct ExpandAndApplyResult_<Func, Tuple<T...>> {
jpayne@69:   typedef decltype(instance<Func>()(instance<T&&>()...)) Type;
jpayne@69: };
jpayne@69: template <typename Func, typename... T>
jpayne@69: using ExpandAndApplyResult = typename ExpandAndApplyResult_<Func, Tuple<>, T...>::Type;
jpayne@69: // Computes the expected return type of `expandAndApply()`.
jpayne@69: 
jpayne@69: template <typename Func>
jpayne@69: inline auto expandAndApply(Func&& func) -> ExpandAndApplyResult<Func> {
jpayne@69:   return func();
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename First, typename... Rest>
jpayne@69: struct ExpandAndApplyFunc {
jpayne@69:   Func&& func;
jpayne@69:   First&& first;
jpayne@69:   ExpandAndApplyFunc(Func&& func, First&& first)
jpayne@69:       : func(kj::fwd<Func>(func)), first(kj::fwd<First>(first)) {}
jpayne@69:   template <typename... T>
jpayne@69:   auto operator()(T&&... params)
jpayne@69:       -> decltype(this->func(kj::fwd<First>(first), kj::fwd<T>(params)...)) {
jpayne@69:     return this->func(kj::fwd<First>(first), kj::fwd<T>(params)...);
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename Func, typename First, typename... Rest>
jpayne@69: inline auto expandAndApply(Func&& func, First&& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, First, Rest...> {
jpayne@69: 
jpayne@69:   return expandAndApply(
jpayne@69:       ExpandAndApplyFunc<Func, First, Rest...>(kj::fwd<Func>(func), kj::fwd<First>(first)),
jpayne@69:       kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest>
jpayne@69: inline auto expandAndApply(Func&& func, Tuple<FirstTypes...>&& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, FirstTypes&&..., Rest...> {
jpayne@69:   return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
jpayne@69:       kj::fwd<Func>(func), kj::mv(first), kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest>
jpayne@69: inline auto expandAndApply(Func&& func, Tuple<FirstTypes...>& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
jpayne@69:   return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
jpayne@69:       kj::fwd<Func>(func), first, kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest>
jpayne@69: inline auto expandAndApply(Func&& func, const Tuple<FirstTypes...>& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
jpayne@69:   return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
jpayne@69:       kj::fwd<Func>(func), first, kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest, size_t... indexes>
jpayne@69: inline auto expandAndApplyWithIndexes(
jpayne@69:     Indexes<indexes...>, Func&& func, Tuple<FirstTypes...>&& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, FirstTypes&&..., Rest...> {
jpayne@69:   return expandAndApply(kj::fwd<Func>(func), kj::mv(getImpl<indexes>(first))...,
jpayne@69:                         kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... FirstTypes, typename... Rest, size_t... indexes>
jpayne@69: inline auto expandAndApplyWithIndexes(
jpayne@69:     Indexes<indexes...>, Func&& func, const Tuple<FirstTypes...>& first, Rest&&... rest)
jpayne@69:     -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
jpayne@69:   return expandAndApply(kj::fwd<Func>(func), getImpl<indexes>(first)...,
jpayne@69:                        kj::fwd<Rest>(rest)...);
jpayne@69: }
jpayne@69: 
jpayne@69: struct MakeTupleFunc {
jpayne@69:   template <typename... Params>
jpayne@69:   Tuple<Decay<Params>...> operator()(Params&&... params) {
jpayne@69:     return Tuple<Decay<Params>...>(kj::fwd<Params>(params)...);
jpayne@69:   }
jpayne@69:   template <typename Param>
jpayne@69:   Decay<Param> operator()(Param&& param) {
jpayne@69:     return kj::fwd<Param>(param);
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: struct MakeRefTupleFunc {
jpayne@69:   template <typename... Params>
jpayne@69:   Tuple<Params...> operator()(Params&&... params) {
jpayne@69:     return Tuple<Params...>(kj::fwd<Params>(params)...);
jpayne@69:   }
jpayne@69:   template <typename Param>
jpayne@69:   Param operator()(Param&& param) {
jpayne@69:     return kj::fwd<Param>(param);
jpayne@69:   }
jpayne@69: };
jpayne@69: 
jpayne@69: }  // namespace _ (private)
jpayne@69: 
jpayne@69: template <typename... T> struct Tuple_ { typedef _::Tuple<T...> Type; };
jpayne@69: template <typename T> struct Tuple_<T> { typedef T Type; };
jpayne@69: 
jpayne@69: template <typename... T> using Tuple = typename Tuple_<T...>::Type;
jpayne@69: // Tuple type.  `Tuple<T>` (i.e. a single-element tuple) is a synonym for `T`.  Tuples of size
jpayne@69: // other than 1 expand to an internal type.  Either way, you can construct a Tuple using
jpayne@69: // `kj::tuple(...)`, get an element by index `i` using `kj::get<i>(myTuple)`, and expand the tuple
jpayne@69: // as arguments to a function using `kj::apply(func, myTuple)`.
jpayne@69: //
jpayne@69: // Tuples are always flat -- that is, no element of a Tuple is ever itself a Tuple.  If you
jpayne@69: // construct a tuple from other tuples, the elements are flattened and concatenated.
jpayne@69: 
jpayne@69: template <typename... Params>
jpayne@69: inline auto tuple(Params&&... params)
jpayne@69:     -> decltype(_::expandAndApply(_::MakeTupleFunc(), kj::fwd<Params>(params)...)) {
jpayne@69:   // Construct a new tuple from the given values.  Any tuples in the argument list will be
jpayne@69:   // flattened into the result.
jpayne@69:   return _::expandAndApply(_::MakeTupleFunc(), kj::fwd<Params>(params)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename... Params>
jpayne@69: inline auto refTuple(Params&&... params)
jpayne@69:     -> decltype(_::expandAndApply(_::MakeRefTupleFunc(), kj::fwd<Params>(params)...)) {
jpayne@69:   // Like tuple(), but if the params include lvalue references, they will be captured as
jpayne@69:   // references. rvalue references will still be captured as whole values (moved).
jpayne@69:   return _::expandAndApply(_::MakeRefTupleFunc(), kj::fwd<Params>(params)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <size_t index, typename Tuple>
jpayne@69: inline auto get(Tuple&& tuple) -> decltype(_::getImpl<index>(kj::fwd<Tuple>(tuple))) {
jpayne@69:   // Unpack and return the tuple element at the given index.  The index is specified as a template
jpayne@69:   // parameter, e.g. `kj::get<3>(myTuple)`.
jpayne@69:   return _::getImpl<index>(kj::fwd<Tuple>(tuple));
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename Func, typename... Params>
jpayne@69: inline auto apply(Func&& func, Params&&... params)
jpayne@69:     -> decltype(_::expandAndApply(kj::fwd<Func>(func), kj::fwd<Params>(params)...)) {
jpayne@69:   // Apply a function to some arguments, expanding tuples into separate arguments.
jpayne@69:   return _::expandAndApply(kj::fwd<Func>(func), kj::fwd<Params>(params)...);
jpayne@69: }
jpayne@69: 
jpayne@69: template <typename T> struct TupleSize_ { static constexpr size_t size = 1; };
jpayne@69: template <typename... T> struct TupleSize_<_::Tuple<T...>> {
jpayne@69:   static constexpr size_t size = sizeof...(T);
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: constexpr size_t tupleSize() { return TupleSize_<T>::size; }
jpayne@69: // Returns size of the tuple T.
jpayne@69: 
jpayne@69: template <typename T, typename Tuple>
jpayne@69: struct IndexOfType_;
jpayne@69: template <typename T, typename Tuple>
jpayne@69: struct HasType_ {
jpayne@69:   static constexpr bool value = false;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T>
jpayne@69: struct IndexOfType_<T, T> {
jpayne@69:   static constexpr size_t value = 0;
jpayne@69: };
jpayne@69: template <typename T>
jpayne@69: struct HasType_<T, T> {
jpayne@69:   static constexpr bool value = true;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename... U>
jpayne@69: struct IndexOfType_<T, _::Tuple<T, U...>> {
jpayne@69:   static constexpr size_t value = 0;
jpayne@69:   static_assert(!HasType_<T, _::Tuple<U...>>::value,
jpayne@69:       "requested type appears multiple times in tuple");
jpayne@69: };
jpayne@69: template <typename T, typename... U>
jpayne@69: struct HasType_<T, _::Tuple<T, U...>> {
jpayne@69:   static constexpr bool value = true;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename U, typename... V>
jpayne@69: struct IndexOfType_<T, _::Tuple<U, V...>> {
jpayne@69:   static constexpr size_t value = IndexOfType_<T, _::Tuple<V...>>::value + 1;
jpayne@69: };
jpayne@69: template <typename T, typename U, typename... V>
jpayne@69: struct HasType_<T, _::Tuple<U, V...>> {
jpayne@69:   static constexpr bool value = HasType_<T, _::Tuple<V...>>::value;
jpayne@69: };
jpayne@69: 
jpayne@69: template <typename T, typename U>
jpayne@69: inline constexpr size_t indexOfType() {
jpayne@69:   static_assert(HasType_<T, U>::value, "type not present");
jpayne@69:   return IndexOfType_<T, U>::value;
jpayne@69: }
jpayne@69: 
jpayne@69: template <size_t i, typename T>
jpayne@69: struct TypeOfIndex_;
jpayne@69: template <typename T>
jpayne@69: struct TypeOfIndex_<0, T> {
jpayne@69:   typedef T Type;
jpayne@69: };
jpayne@69: template <size_t i, typename T, typename... U>
jpayne@69: struct TypeOfIndex_<i, _::Tuple<T, U...>>
jpayne@69:     : public TypeOfIndex_<i - 1, _::Tuple<U...>> {};
jpayne@69: template <typename T, typename... U>
jpayne@69: struct TypeOfIndex_<0, _::Tuple<T, U...>> {
jpayne@69:   typedef T Type;
jpayne@69: };
jpayne@69: 
jpayne@69: template <size_t i, typename Tuple>
jpayne@69: using TypeOfIndex = typename TypeOfIndex_<i, Tuple>::Type;
jpayne@69: 
jpayne@69: }  // namespace kj
jpayne@69: 
jpayne@69: KJ_END_HEADER