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61d9aacb68
It's currently fairly difficult to perform some operation on each member of a tuple. This is a particular issue in the context of adding a cycle collection helper, where we need to perform traverse and unlink operations on each member of a tuple, and don't have a way to do so without several layers of templates. This patch adds a ForEach function which will call a function on each element of the tuple. This would typically be used with a lambda function with a single `auto&` argument. --HG-- extra : rebase_source : 577f7c823ab7ee8d1fdedfbd26393c1f1664b965
530 lines
17 KiB
C++
530 lines
17 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* A variadic tuple class. */
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#ifndef mozilla_Tuple_h
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#define mozilla_Tuple_h
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#include "mozilla/Move.h"
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#include "mozilla/Pair.h"
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#include "mozilla/TemplateLib.h"
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#include "mozilla/TypeTraits.h"
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#include <stddef.h>
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#include <utility>
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namespace mozilla {
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namespace detail {
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/*
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* A helper class that allows passing around multiple variadic argument lists
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* by grouping them.
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*/
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template<typename... Ts>
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struct Group;
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/*
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* CheckConvertibility checks whether each type in a source pack of types
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* is convertible to the corresponding type in a target pack of types.
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*
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* It is intended to be invoked like this:
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* CheckConvertibility<Group<SourceTypes...>, Group<TargetTypes...>>
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* 'Group' is used to separate types in the two packs (otherwise if we just
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* wrote 'CheckConvertibility<SourceTypes..., TargetTypes...', it couldn't
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* know where the first pack ends and the second begins).
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*
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* Note that we need to check explicitly that the two packs are of the same
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* size, because attempting to simultaneously expand two parameter packs
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* is an error (and it would be a hard error, because it wouldn't be in the
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* immediate context of the caller).
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*/
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template<typename Source, typename Target, bool SameSize>
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struct CheckConvertibilityImpl;
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template<typename Source, typename Target>
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struct CheckConvertibilityImpl<Source, Target, false>
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: FalseType {};
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template<typename... SourceTypes, typename... TargetTypes>
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struct CheckConvertibilityImpl<Group<SourceTypes...>, Group<TargetTypes...>, true>
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: IntegralConstant<bool, tl::And<IsConvertible<SourceTypes, TargetTypes>::value...>::value> { };
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template<typename Source, typename Target>
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struct CheckConvertibility;
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template<typename... SourceTypes, typename... TargetTypes>
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struct CheckConvertibility<Group<SourceTypes...>, Group<TargetTypes...>>
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: CheckConvertibilityImpl<Group<SourceTypes...>, Group<TargetTypes...>,
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sizeof...(SourceTypes) == sizeof...(TargetTypes)> { };
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/*
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* TupleImpl is a helper class used to implement mozilla::Tuple.
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* It represents one node in a recursive inheritance hierarchy.
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* 'Index' is the 0-based index of the tuple element stored in this node;
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* 'Elements...' are the types of the elements stored in this node and its
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* base classes.
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*
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* Example:
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* Tuple<int, float, char> inherits from
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* TupleImpl<0, int, float, char>, which stores the 'int' and inherits from
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* TupleImpl<1, float, char>, which stores the 'float' and inherits from
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* TupleImpl<2, char>, which stores the 'char' and inherits from
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* TupleImpl<3>, which stores nothing and terminates the recursion.
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*
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* The purpose of the 'Index' parameter is to allow efficient index-based
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* access to a tuple element: given a tuple, and an index 'I' that we wish to
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* access, we can cast the tuple to the base which stores the I'th element
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* by performing template argument deduction against 'TupleImpl<I, E...>',
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* where 'I' is specified explicitly and 'E...' is deduced (this is what the
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* non-member 'Get<N>(t)' function does).
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*
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* This implementation strategy is borrowed from libstdc++'s std::tuple
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* implementation.
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*/
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template<std::size_t Index, typename... Elements>
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struct TupleImpl;
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/*
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* The base case of the inheritance recursion (and also the implementation
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* of an empty tuple).
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*/
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template<std::size_t Index>
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struct TupleImpl<Index> {
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bool operator==(const TupleImpl<Index>& aOther) const
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{
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return true;
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}
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template <typename F>
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void ForEach(const F& aFunc) {}
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};
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/*
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* One node of the recursive inheritance hierarchy. It stores the element at
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* index 'Index' of a tuple, of type 'HeadT', and inherits from the nodes
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* that store the remaining elements, of types 'TailT...'.
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*/
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template<std::size_t Index, typename HeadT, typename... TailT>
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struct TupleImpl<Index, HeadT, TailT...>
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: public TupleImpl<Index + 1, TailT...>
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{
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typedef TupleImpl<Index + 1, TailT...> Base;
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// Accessors for the head and the tail.
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// These are static, because the intended usage is for the caller to,
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// given a tuple, obtain the type B of the base class which stores the
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// element of interest, and then call B::Head(tuple) to access it.
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// (Tail() is mostly for internal use, but is exposed for consistency.)
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static HeadT& Head(TupleImpl& aTuple) { return aTuple.mHead; }
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static const HeadT& Head(const TupleImpl& aTuple) { return aTuple.mHead; }
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static Base& Tail(TupleImpl& aTuple) { return aTuple; }
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static const Base& Tail(const TupleImpl& aTuple) { return aTuple; }
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TupleImpl() : Base(), mHead() { }
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// Construct from const references to the elements.
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explicit TupleImpl(const HeadT& aHead, const TailT&... aTail)
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: Base(aTail...), mHead(aHead) { }
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// Construct from objects that are convertible to the elements.
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// This constructor is enabled only when the argument types are actually
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// convertible to the element types, otherwise it could become a better
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// match for certain invocations than the copy constructor.
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template <typename OtherHeadT, typename... OtherTailT,
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typename = typename EnableIf<
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CheckConvertibility<
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Group<OtherHeadT, OtherTailT...>,
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Group<HeadT, TailT...>>::value>::Type>
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explicit TupleImpl(OtherHeadT&& aHead, OtherTailT&&... aTail)
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: Base(std::forward<OtherTailT>(aTail)...), mHead(std::forward<OtherHeadT>(aHead)) { }
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// Copy and move constructors.
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// We'd like to use '= default' to implement these, but MSVC 2013's support
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// for '= default' is incomplete and this doesn't work.
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TupleImpl(const TupleImpl& aOther)
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: Base(Tail(aOther))
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, mHead(Head(aOther)) {}
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TupleImpl(TupleImpl&& aOther)
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: Base(std::move(Tail(aOther)))
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, mHead(std::forward<HeadT>(Head(aOther))) {}
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// Assign from a tuple whose elements are convertible to the elements
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// of this tuple.
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template <typename... OtherElements,
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typename = typename EnableIf<
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sizeof...(OtherElements) == sizeof...(TailT) + 1>::Type>
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TupleImpl& operator=(const TupleImpl<Index, OtherElements...>& aOther)
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{
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typedef TupleImpl<Index, OtherElements...> OtherT;
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Head(*this) = OtherT::Head(aOther);
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Tail(*this) = OtherT::Tail(aOther);
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return *this;
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}
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template <typename... OtherElements,
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typename = typename EnableIf<
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sizeof...(OtherElements) == sizeof...(TailT) + 1>::Type>
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TupleImpl& operator=(TupleImpl<Index, OtherElements...>&& aOther)
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{
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typedef TupleImpl<Index, OtherElements...> OtherT;
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Head(*this) = std::move(OtherT::Head(aOther));
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Tail(*this) = std::move(OtherT::Tail(aOther));
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return *this;
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}
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// Copy and move assignment operators.
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TupleImpl& operator=(const TupleImpl& aOther)
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{
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Head(*this) = Head(aOther);
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Tail(*this) = Tail(aOther);
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return *this;
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}
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TupleImpl& operator=(TupleImpl&& aOther)
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{
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Head(*this) = std::move(Head(aOther));
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Tail(*this) = std::move(Tail(aOther));
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return *this;
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}
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bool operator==(const TupleImpl& aOther) const
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{
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return Head(*this) == Head(aOther) && Tail(*this) == Tail(aOther);
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}
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template <typename F>
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void ForEach(const F& aFunc) const &
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{
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aFunc(Head(*this));
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Tail(*this).ForEach(aFunc);
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}
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template <typename F>
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void ForEach(const F& aFunc) &
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{
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aFunc(Head(*this));
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Tail(*this).ForEach(aFunc);
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}
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template <typename F>
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void ForEach(const F& aFunc) &&
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{
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aFunc(std::move(Head(*this)));
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std::move(Tail(*this)).ForEach(aFunc);
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}
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private:
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HeadT mHead; // The element stored at this index in the tuple.
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};
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} // namespace detail
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/**
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* Tuple is a class that stores zero or more objects, whose types are specified
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* as template parameters. It can be thought of as a generalization of Pair,
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* (which can be thought of as a 2-tuple).
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*
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* Tuple allows index-based access to its elements (with the index having to be
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* known at compile time) via the non-member function 'Get<N>(tuple)'.
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*/
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template<typename... Elements>
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class Tuple : public detail::TupleImpl<0, Elements...>
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{
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typedef detail::TupleImpl<0, Elements...> Impl;
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public:
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// The constructors and assignment operators here are simple wrappers
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// around those in TupleImpl.
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Tuple() : Impl() { }
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explicit Tuple(const Elements&... aElements) : Impl(aElements...) { }
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// Here, we can't just use 'typename... OtherElements' because MSVC will give
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// a warning "C4520: multiple default constructors specified" (even if no one
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// actually instantiates the constructor with an empty parameter pack -
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// that's probably a bug) and we compile with warnings-as-errors.
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template <typename OtherHead, typename... OtherTail,
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typename = typename EnableIf<
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detail::CheckConvertibility<
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detail::Group<OtherHead, OtherTail...>,
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detail::Group<Elements...>>::value>::Type>
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explicit Tuple(OtherHead&& aHead, OtherTail&&... aTail)
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: Impl(std::forward<OtherHead>(aHead), std::forward<OtherTail>(aTail)...) { }
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Tuple(const Tuple& aOther) : Impl(aOther) { }
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Tuple(Tuple&& aOther) : Impl(std::move(aOther)) { }
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template <typename... OtherElements,
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typename = typename EnableIf<
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sizeof...(OtherElements) == sizeof...(Elements)>::Type>
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Tuple& operator=(const Tuple<OtherElements...>& aOther)
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{
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static_cast<Impl&>(*this) = aOther;
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return *this;
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}
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template <typename... OtherElements,
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typename = typename EnableIf<
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sizeof...(OtherElements) == sizeof...(Elements)>::Type>
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Tuple& operator=(Tuple<OtherElements...>&& aOther)
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{
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static_cast<Impl&>(*this) = std::move(aOther);
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return *this;
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}
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Tuple& operator=(const Tuple& aOther)
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{
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static_cast<Impl&>(*this) = aOther;
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return *this;
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}
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Tuple& operator=(Tuple&& aOther)
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{
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static_cast<Impl&>(*this) = std::move(aOther);
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return *this;
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}
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bool operator==(const Tuple& aOther) const
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{
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return static_cast<const Impl&>(*this) == static_cast<const Impl&>(aOther);
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}
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};
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/**
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* Specialization of Tuple for two elements.
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* This is created to support construction and assignment from a Pair or std::pair.
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*/
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template <typename A, typename B>
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class Tuple<A, B> : public detail::TupleImpl<0, A, B>
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{
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typedef detail::TupleImpl<0, A, B> Impl;
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public:
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// The constructors and assignment operators here are simple wrappers
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// around those in TupleImpl.
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Tuple() : Impl() { }
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explicit Tuple(const A& aA, const B& aB) : Impl(aA, aB) { }
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template <typename AArg, typename BArg,
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typename = typename EnableIf<
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detail::CheckConvertibility<
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detail::Group<AArg, BArg>,
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detail::Group<A, B>>::value>::Type>
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explicit Tuple(AArg&& aA, BArg&& aB)
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: Impl(std::forward<AArg>(aA), std::forward<BArg>(aB)) { }
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Tuple(const Tuple& aOther) : Impl(aOther) { }
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Tuple(Tuple&& aOther) : Impl(std::move(aOther)) { }
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explicit Tuple(const Pair<A, B>& aOther)
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: Impl(aOther.first(), aOther.second()) { }
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explicit Tuple(Pair<A, B>&& aOther) : Impl(std::forward<A>(aOther.first()),
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std::forward<B>(aOther.second())) { }
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explicit Tuple(const std::pair<A, B>& aOther)
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: Impl(aOther.first, aOther.second) { }
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explicit Tuple(std::pair<A, B>&& aOther) : Impl(std::forward<A>(aOther.first),
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std::forward<B>(aOther.second)) { }
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template <typename AArg, typename BArg>
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Tuple& operator=(const Tuple<AArg, BArg>& aOther)
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{
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static_cast<Impl&>(*this) = aOther;
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return *this;
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}
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template <typename AArg, typename BArg>
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Tuple& operator=(Tuple<AArg, BArg>&& aOther)
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{
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static_cast<Impl&>(*this) = std::move(aOther);
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return *this;
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}
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Tuple& operator=(const Tuple& aOther)
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{
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static_cast<Impl&>(*this) = aOther;
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return *this;
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}
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Tuple& operator=(Tuple&& aOther)
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{
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static_cast<Impl&>(*this) = std::move(aOther);
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return *this;
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}
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template <typename AArg, typename BArg>
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Tuple& operator=(const Pair<AArg, BArg>& aOther)
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{
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Impl::Head(*this) = aOther.first();
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Impl::Tail(*this).Head(*this) = aOther.second();
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return *this;
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}
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template <typename AArg, typename BArg>
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Tuple& operator=(Pair<AArg, BArg>&& aOther)
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{
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Impl::Head(*this) = std::forward<AArg>(aOther.first());
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Impl::Tail(*this).Head(*this) = std::forward<BArg>(aOther.second());
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return *this;
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}
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template <typename AArg, typename BArg>
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Tuple& operator=(const std::pair<AArg, BArg>& aOther)
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{
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Impl::Head(*this) = aOther.first;
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Impl::Tail(*this).Head(*this) = aOther.second;
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return *this;
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}
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template <typename AArg, typename BArg>
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Tuple& operator=(std::pair<AArg, BArg>&& aOther)
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{
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Impl::Head(*this) = std::forward<AArg>(aOther.first);
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Impl::Tail(*this).Head(*this) = std::forward<BArg>(aOther.second);
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return *this;
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}
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};
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/**
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* Specialization of Tuple for zero arguments.
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* This is necessary because if the primary template were instantiated with
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* an empty parameter pack, the 'Tuple(Elements...)' constructors would
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* become illegal overloads of the default constructor.
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*/
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template <>
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class Tuple<> {};
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namespace detail {
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/*
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* Helper functions for implementing Get<N>(tuple).
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* These functions take a TupleImpl<Index, Elements...>, with Index being
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* explicitly specified, and Elements being deduced. By passing a Tuple
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* object as argument, template argument deduction will do its magic and
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* cast the tuple to the base class which stores the element at Index.
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*/
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// Const reference version.
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template<std::size_t Index, typename... Elements>
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auto TupleGetHelper(TupleImpl<Index, Elements...>& aTuple)
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-> decltype(TupleImpl<Index, Elements...>::Head(aTuple))
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{
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return TupleImpl<Index, Elements...>::Head(aTuple);
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}
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// Non-const reference version.
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template<std::size_t Index, typename... Elements>
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auto TupleGetHelper(const TupleImpl<Index, Elements...>& aTuple)
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-> decltype(TupleImpl<Index, Elements...>::Head(aTuple))
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{
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return TupleImpl<Index, Elements...>::Head(aTuple);
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}
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} // namespace detail
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/**
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* Index-based access to an element of a tuple.
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* The syntax is Get<Index>(tuple). The index is zero-based.
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*
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* Example:
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*
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* Tuple<int, float, char> t;
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* ...
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* float f = Get<1>(t);
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*/
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// Non-const reference version.
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template<std::size_t Index, typename... Elements>
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auto Get(Tuple<Elements...>& aTuple)
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-> decltype(detail::TupleGetHelper<Index>(aTuple))
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{
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return detail::TupleGetHelper<Index>(aTuple);
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}
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// Const reference version.
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template<std::size_t Index, typename... Elements>
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auto Get(const Tuple<Elements...>& aTuple)
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-> decltype(detail::TupleGetHelper<Index>(aTuple))
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{
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return detail::TupleGetHelper<Index>(aTuple);
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}
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// Rvalue reference version.
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template<std::size_t Index, typename... Elements>
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auto Get(Tuple<Elements...>&& aTuple)
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-> decltype(std::move(mozilla::Get<Index>(aTuple)))
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{
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// We need a 'mozilla::' qualification here to avoid
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// name lookup only finding the current function.
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return std::move(mozilla::Get<Index>(aTuple));
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}
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/**
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* Helpers which call a function for each member of the tuple in turn. This will
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* typically be used with a lambda function with an `auto&` argument:
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*
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* Tuple<Foo*, Bar*, SmartPtr<Baz>> tuple{a, b, c};
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*
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* ForEach(tuple, [](auto& aElem) {
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* aElem = nullptr;
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* });
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*/
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template <typename F>
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inline void
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ForEach(const Tuple<>& aTuple, const F& aFunc)
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{
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}
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template <typename F>
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inline void
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ForEach(Tuple<>& aTuple, const F& aFunc)
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{
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}
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template <typename F, typename... Elements>
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void
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ForEach(const Tuple<Elements...>& aTuple, const F& aFunc)
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{
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aTuple.ForEach(aTuple, aFunc);
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}
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template <typename F, typename... Elements>
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void
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ForEach(Tuple<Elements...>& aTuple, const F& aFunc)
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|
{
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|
aTuple.ForEach(aFunc);
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|
}
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|
|
|
template <typename F, typename... Elements>
|
|
void
|
|
ForEach(Tuple<Elements...>&& aTuple, const F& aFunc)
|
|
{
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|
std::forward<Tuple<Elements...>>(aTuple).ForEach(aFunc);
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|
}
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|
|
|
/**
|
|
* 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<typename Decay<Elements>::Type...>
|
|
MakeTuple(Elements&&... aElements)
|
|
{
|
|
return Tuple<typename Decay<Elements>::Type...>(std::forward<Elements>(aElements)...);
|
|
}
|
|
|
|
/**
|
|
* 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 */
|