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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* A variadic tuple class. */
#ifndef mozilla_Tuple_h
#define mozilla_Tuple_h
#include <stddef.h>
#include <type_traits>
#include <utility>
#include "mozilla/CompactPair.h"
#include "mozilla/TemplateLib.h"
namespace mozilla {
namespace detail {
/*
* A helper class that allows passing around multiple variadic argument lists
* by grouping them.
*/
template <typename... Ts>
struct Group;
/*
* CheckConvertibility checks whether each type in a source pack of types
* is convertible to the corresponding type in a target pack of types.
*
* It is intended to be invoked like this:
* CheckConvertibility<Group<SourceTypes...>, Group<TargetTypes...>>
* 'Group' is used to separate types in the two packs (otherwise if we just
* wrote 'CheckConvertibility<SourceTypes..., TargetTypes...', it couldn't
* know where the first pack ends and the second begins).
*
* Note that we need to check explicitly that the two packs are of the same
* size, because attempting to simultaneously expand two parameter packs
* is an error (and it would be a hard error, because it wouldn't be in the
* immediate context of the caller).
*/
template <typename Source, typename Target, bool SameSize>
struct CheckConvertibilityImpl;
template <typename Source, typename Target>
struct CheckConvertibilityImpl<Source, Target, false> : std::false_type {};
template <typename... SourceTypes, typename... TargetTypes>
struct CheckConvertibilityImpl<Group<SourceTypes...>, Group<TargetTypes...>,
true>
: std::integral_constant<
bool,
tl::And<std::is_convertible_v<SourceTypes, TargetTypes>...>::value> {
};
template <typename Source, typename Target>
struct CheckConvertibility;
template <typename... SourceTypes, typename... TargetTypes>
struct CheckConvertibility<Group<SourceTypes...>, Group<TargetTypes...>>
: CheckConvertibilityImpl<Group<SourceTypes...>, Group<TargetTypes...>,
sizeof...(SourceTypes) ==
sizeof...(TargetTypes)> {};
/*
* Helper type for Tie(args...) to allow ignoring specific elements
* during Tie unpacking. Supports assignment from any type.
*
* Not for direct usage; instead, use mozilla::Ignore in calls to Tie.
*/
struct IgnoreImpl {
template <typename T>
constexpr const IgnoreImpl& operator=(const T&) const {
return *this;
}
};
/*
* TupleImpl is a helper class used to implement mozilla::Tuple.
* It represents one node in a recursive inheritance hierarchy.
* 'Index' is the 0-based index of the tuple element stored in this node;
* 'Elements...' are the types of the elements stored in this node and its
* base classes.
*
* Example:
* Tuple<int, float, char> inherits from
* TupleImpl<0, int, float, char>, which stores the 'int' and inherits from
* TupleImpl<1, float, char>, which stores the 'float' and inherits from
* TupleImpl<2, char>, which stores the 'char' and inherits from
* TupleImpl<3>, which stores nothing and terminates the recursion.
*
* The purpose of the 'Index' parameter is to allow efficient index-based
* access to a tuple element: given a tuple, and an index 'I' that we wish to
* access, we can cast the tuple to the base which stores the I'th element
* by performing template argument deduction against 'TupleImpl<I, E...>',
* where 'I' is specified explicitly and 'E...' is deduced (this is what the
* non-member 'Get<N>(t)' function does).
*
* This implementation strategy is borrowed from libstdc++'s std::tuple
* implementation.
*/
template <std::size_t Index, typename... Elements>
struct TupleImpl;
/*
* The base case of the inheritance recursion (and also the implementation
* of an empty tuple).
*/
template <std::size_t Index>
struct TupleImpl<Index> {
bool operator==(const TupleImpl<Index>& aOther) const { return true; }
template <typename F>
void ForEach(const F& aFunc) const {}
};
/*
* One node of the recursive inheritance hierarchy. It stores the element at
* index 'Index' of a tuple, of type 'HeadT', and inherits from the nodes
* that store the remaining elements, of types 'TailT...'.
*/
template <std::size_t Index, typename HeadT, typename... TailT>
struct TupleImpl<Index, HeadT, TailT...>
: public TupleImpl<Index + 1, TailT...> {
typedef TupleImpl<Index + 1, TailT...> Base;
// Accessors for the head and the tail.
// These are static, because the intended usage is for the caller to,
// given a tuple, obtain the type B of the base class which stores the
// element of interest, and then call B::Head(tuple) to access it.
// (Tail() is mostly for internal use, but is exposed for consistency.)
static HeadT& Head(TupleImpl& aTuple) { return aTuple.mHead; }
static const HeadT& Head(const TupleImpl& aTuple) { return aTuple.mHead; }
static Base& Tail(TupleImpl& aTuple) { return aTuple; }
static const Base& Tail(const TupleImpl& aTuple) { return aTuple; }
TupleImpl() : Base(), mHead() {}
// Construct from const references to the elements.
explicit TupleImpl(const HeadT& aHead, const TailT&... aTail)
: Base(aTail...), mHead(aHead) {}
// Construct from objects that are convertible to the elements.
// This constructor is enabled only when the argument types are actually
// convertible to the element types, otherwise it could become a better
// match for certain invocations than the copy constructor.
template <
typename OtherHeadT, typename... OtherTailT,
typename = std::enable_if_t<CheckConvertibility<
Group<OtherHeadT, OtherTailT...>, Group<HeadT, TailT...>>::value>>
explicit TupleImpl(OtherHeadT&& aHead, OtherTailT&&... aTail)
: Base(std::forward<OtherTailT>(aTail)...),
mHead(std::forward<OtherHeadT>(aHead)) {}
// Copy and move constructors.
// We'd like to use '= default' to implement these, but MSVC 2013's support
// for '= default' is incomplete and this doesn't work.
TupleImpl(const TupleImpl& aOther)
: Base(Tail(aOther)), mHead(Head(aOther)) {}
TupleImpl(TupleImpl&& aOther)
: Base(std::move(Tail(aOther))),
mHead(std::forward<HeadT>(Head(aOther))) {}
// Assign from a tuple whose elements are convertible to the elements
// of this tuple.
template <typename... OtherElements,
typename = std::enable_if_t<sizeof...(OtherElements) ==
sizeof...(TailT) + 1>>
TupleImpl& operator=(const TupleImpl<Index, OtherElements...>& aOther) {
typedef TupleImpl<Index, OtherElements...> OtherT;
Head(*this) = OtherT::Head(aOther);
Tail(*this) = OtherT::Tail(aOther);
return *this;
}
template <typename... OtherElements,
typename = std::enable_if_t<sizeof...(OtherElements) ==
sizeof...(TailT) + 1>>
TupleImpl& operator=(TupleImpl<Index, OtherElements...>&& aOther) {
typedef TupleImpl<Index, OtherElements...> OtherT;
Head(*this) = std::move(OtherT::Head(aOther));
Tail(*this) = std::move(OtherT::Tail(aOther));
return *this;
}
// Copy and move assignment operators.
TupleImpl& operator=(const TupleImpl& aOther) {
Head(*this) = Head(aOther);
Tail(*this) = Tail(aOther);
return *this;
}
TupleImpl& operator=(TupleImpl&& aOther) {
Head(*this) = std::move(Head(aOther));
Tail(*this) = std::move(Tail(aOther));
return *this;
}
bool operator==(const TupleImpl& aOther) const {
return Head(*this) == Head(aOther) && Tail(*this) == Tail(aOther);
}
template <typename F>
void ForEach(const F& aFunc) const& {
aFunc(Head(*this));
Tail(*this).ForEach(aFunc);
}
template <typename F>
void ForEach(const F& aFunc) & {
aFunc(Head(*this));
Tail(*this).ForEach(aFunc);
}
template <typename F>
void ForEach(const F& aFunc) && {
aFunc(std::move(Head(*this)));
std::move(Tail(*this)).ForEach(aFunc);
}
private:
HeadT mHead; // The element stored at this index in the tuple.
};
} // namespace detail
/**
* Tuple is a class that stores zero or more objects, whose types are specified
* as template parameters. It can be thought of as a generalization of
* std::pair, (which can be thought of as a 2-tuple).
*
* Tuple allows index-based access to its elements (with the index having to be
* known at compile time) via the non-member function 'Get<N>(tuple)'.
*/
template <typename... Elements>
class Tuple : public detail::TupleImpl<0, Elements...> {
typedef detail::TupleImpl<0, Elements...> Impl;
public:
// The constructors and assignment operators here are simple wrappers
// around those in TupleImpl.
Tuple() : Impl() {}
explicit Tuple(const Elements&... aElements) : Impl(aElements...) {}
// Here, we can't just use 'typename... OtherElements' because MSVC will give
// a warning "C4520: multiple default constructors specified" (even if no one
// actually instantiates the constructor with an empty parameter pack -
// that's probably a bug) and we compile with warnings-as-errors.
template <typename OtherHead, typename... OtherTail,
typename = std::enable_if_t<detail::CheckConvertibility<
detail::Group<OtherHead, OtherTail...>,
detail::Group<Elements...>>::value>>
explicit Tuple(OtherHead&& aHead, OtherTail&&... aTail)
: Impl(std::forward<OtherHead>(aHead),
std::forward<OtherTail>(aTail)...) {}
Tuple(const Tuple& aOther) : Impl(aOther) {}
Tuple(Tuple&& aOther) : Impl(std::move(aOther)) {}
template <typename... OtherElements,
typename = std::enable_if_t<sizeof...(OtherElements) ==
sizeof...(Elements)>>
Tuple& operator=(const Tuple<OtherElements...>& aOther) {
static_cast<Impl&>(*this) = aOther;
return *this;
}
template <typename... OtherElements,
typename = std::enable_if_t<sizeof...(OtherElements) ==
sizeof...(Elements)>>
Tuple& operator=(Tuple<OtherElements...>&& aOther) {
static_cast<Impl&>(*this) = std::move(aOther);
return *this;
}
Tuple& operator=(const Tuple& aOther) {
static_cast<Impl&>(*this) = aOther;
return *this;
}
Tuple& operator=(Tuple&& aOther) {
static_cast<Impl&>(*this) = std::move(aOther);
return *this;
}
bool operator==(const Tuple& aOther) const {
return static_cast<const Impl&>(*this) == static_cast<const Impl&>(aOther);
}
};
/**
* Specialization of Tuple for two elements.
* This is created to support construction and assignment from a CompactPair or
* std::pair.
*/
template <typename A, typename B>
class Tuple<A, B> : public detail::TupleImpl<0, A, B> {
typedef detail::TupleImpl<0, A, B> Impl;
public:
// The constructors and assignment operators here are simple wrappers
// around those in TupleImpl.
Tuple() : Impl() {}
explicit Tuple(const A& aA, const B& aB) : Impl(aA, aB) {}
template <typename AArg, typename BArg,
typename = std::enable_if_t<detail::CheckConvertibility<
detail::Group<AArg, BArg>, detail::Group<A, B>>::value>>
explicit Tuple(AArg&& aA, BArg&& aB)
: Impl(std::forward<AArg>(aA), std::forward<BArg>(aB)) {}
Tuple(const Tuple& aOther) : Impl(aOther) {}
Tuple(Tuple&& aOther) : Impl(std::move(aOther)) {}
explicit Tuple(const CompactPair<A, B>& aOther)
: Impl(aOther.first(), aOther.second()) {}
explicit Tuple(CompactPair<A, B>&& aOther)
: Impl(std::forward<A>(aOther.first()),
std::forward<B>(aOther.second())) {}
explicit Tuple(const std::pair<A, B>& aOther)
: Impl(aOther.first, aOther.second) {}
explicit Tuple(std::pair<A, B>&& aOther)
: Impl(std::forward<A>(aOther.first), std::forward<B>(aOther.second)) {}
template <typename AArg, typename BArg>
Tuple& operator=(const Tuple<AArg, BArg>& aOther) {
static_cast<Impl&>(*this) = aOther;
return *this;
}
template <typename AArg, typename BArg>
Tuple& operator=(Tuple<AArg, BArg>&& aOther) {
static_cast<Impl&>(*this) = std::move(aOther);
return *this;
}
Tuple& operator=(const Tuple& aOther) {
static_cast<Impl&>(*this) = aOther;
return *this;
}
Tuple& operator=(Tuple&& aOther) {
static_cast<Impl&>(*this) = std::move(aOther);
return *this;
}
template <typename AArg, typename BArg>
Tuple& operator=(const CompactPair<AArg, BArg>& aOther) {
Impl::Head(*this) = aOther.first();
Impl::Tail(*this).Head(*this) = aOther.second();
return *this;
}
template <typename AArg, typename BArg>
Tuple& operator=(CompactPair<AArg, BArg>&& aOther) {
Impl::Head(*this) = std::forward<AArg>(aOther.first());
Impl::Tail(*this).Head(*this) = std::forward<BArg>(aOther.second());
return *this;
}
template <typename AArg, typename BArg>
Tuple& operator=(const std::pair<AArg, BArg>& aOther) {
Impl::Head(*this) = aOther.first;
Impl::Tail(*this).Head(*this) = aOther.second;
return *this;
}
template <typename AArg, typename BArg>
Tuple& operator=(std::pair<AArg, BArg>&& aOther) {
Impl::Head(*this) = std::forward<AArg>(aOther.first);
Impl::Tail(*this).Head(*this) = std::forward<BArg>(aOther.second);
return *this;
}
};
/**
* Specialization of Tuple for zero arguments.
* This is necessary because if the primary template were instantiated with
* an empty parameter pack, the 'Tuple(Elements...)' constructors would
* become illegal overloads of the default constructor.
*/
template <>
class Tuple<> {};
namespace detail {
/*
* Helper functions for implementing Get<N>(tuple).
* These functions take a TupleImpl<Index, Elements...>, with Index being
* explicitly specified, and Elements being deduced. By passing a Tuple
* object as argument, template argument deduction will do its magic and
* cast the tuple to the base class which stores the element at Index.
*/
// Const reference version.
template <std::size_t Index, typename... Elements>
auto TupleGetHelper(TupleImpl<Index, Elements...>& aTuple)
-> decltype(TupleImpl<Index, Elements...>::Head(aTuple)) {
return TupleImpl<Index, Elements...>::Head(aTuple);
}
// Non-const reference version.
template <std::size_t Index, typename... Elements>
auto TupleGetHelper(const TupleImpl<Index, Elements...>& aTuple)
-> decltype(TupleImpl<Index, Elements...>::Head(aTuple)) {
return TupleImpl<Index, Elements...>::Head(aTuple);
}
} // namespace detail
/**
* Index-based access to an element of a tuple.
* The syntax is Get<Index>(tuple). The index is zero-based.
*
* Example:
*
* Tuple<int, float, char> t;
* ...
* float f = Get<1>(t);
*/
// Non-const reference version.
template <std::size_t Index, typename... Elements>
auto Get(Tuple<Elements...>& aTuple)
-> decltype(detail::TupleGetHelper<Index>(aTuple)) {
return detail::TupleGetHelper<Index>(aTuple);
}
// Const reference version.
template <std::size_t Index, typename... Elements>
auto Get(const Tuple<Elements...>& aTuple)
-> decltype(detail::TupleGetHelper<Index>(aTuple)) {
return detail::TupleGetHelper<Index>(aTuple);
}
// Rvalue reference version.
template <std::size_t Index, typename... Elements>
auto Get(Tuple<Elements...>&& aTuple)
-> decltype(std::move(mozilla::Get<Index>(aTuple))) {
// We need a 'mozilla::' qualification here to avoid
// name lookup only finding the current function.
return std::move(mozilla::Get<Index>(aTuple));
}
/**
* Helpers which call a function for each member of the tuple in turn. This will
* typically be used with a lambda function with an `auto&` argument:
*
* Tuple<Foo*, Bar*, SmartPtr<Baz>> tuple{a, b, c};
*
* ForEach(tuple, [](auto& aElem) {
* aElem = nullptr;
* });
*/
template <typename F>
inline void ForEach(const Tuple<>& aTuple, const F& aFunc) {}
template <typename F>
inline void ForEach(Tuple<>& aTuple, const F& aFunc) {}
template <typename F, typename... Elements>
void ForEach(const Tuple<Elements...>& aTuple, const F& aFunc) {
aTuple.ForEach(aFunc);
}
template <typename F, typename... Elements>
void ForEach(Tuple<Elements...>& aTuple, const F& aFunc) {
aTuple.ForEach(aFunc);
}
template <typename F, typename... Elements>
void ForEach(Tuple<Elements...>&& aTuple, const F& aFunc) {
std::forward<Tuple<Elements...>>(aTuple).ForEach(aFunc);
}
/**
* A convenience function for constructing a tuple out of a sequence of
* values without specifying the type of the tuple.
* The type of the tuple is deduced from the types of its elements.
*
* Example:
*
* auto tuple = MakeTuple(42, 0.5f, 'c'); // has type Tuple<int, float, char>
*/
template <typename... Elements>
inline Tuple<std::decay_t<Elements>...> MakeTuple(Elements&&... aElements) {
return Tuple<std::decay_t<Elements>...>(std::forward<Elements>(aElements)...);
}
/**
* A helper placholder to allow ignoring specific elements during Tie unpacking.
* Can be used with any type and any number of elements in a call to Tie.
*
* Usage of Ignore with Tie is equivalent to using std::ignore with
* std::tie.
*
* Example:
*
* int i;
* float f;
* char c;
* Tie(i, Ignore, f, c, Ignore) = FunctionThatReturnsATuple();
*/
constexpr detail::IgnoreImpl Ignore;
/**
* A convenience function for constructing a tuple of references to a
* sequence of variables. Since assignments to the elements of the tuple
* "go through" to the referenced variables, this can be used to "unpack"
* a tuple into individual variables.
*
* Example:
*
* int i;
* float f;
* char c;
* Tie(i, f, c) = FunctionThatReturnsATuple();
*/
template <typename... Elements>
inline Tuple<Elements&...> Tie(Elements&... aVariables) {
return Tuple<Elements&...>(aVariables...);
}
} // namespace mozilla
#endif /* mozilla_Tuple_h */