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