mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-26 22:32:46 +00:00
ae75c3faa8
Also make CompactPair<A, B> a literal type if A and B are literal types, and add MaybeStorageBase that ought to be used as a basis of MaybeStorage in a follow-up patch. Differential Revision: https://phabricator.services.mozilla.com/D55930
245 lines
8.6 KiB
C++
245 lines
8.6 KiB
C++
/* -*- 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 class holding a pair of objects that tries to conserve storage space. */
|
|
|
|
#ifndef mozilla_CompactPair_h
|
|
#define mozilla_CompactPair_h
|
|
|
|
#include <type_traits>
|
|
#include <tuple>
|
|
#include <utility>
|
|
|
|
#include "mozilla/Attributes.h"
|
|
|
|
namespace mozilla {
|
|
|
|
namespace detail {
|
|
|
|
enum StorageType { AsBase, AsMember };
|
|
|
|
// Optimize storage using the Empty Base Optimization -- that empty base classes
|
|
// don't take up space -- to optimize size when one or the other class is
|
|
// stateless and can be used as a base class.
|
|
//
|
|
// The extra conditions on storage for B are necessary so that CompactPairHelper
|
|
// won't ambiguously inherit from either A or B, such that one or the other base
|
|
// class would be inaccessible.
|
|
template <typename A, typename B,
|
|
detail::StorageType =
|
|
std::is_empty_v<A> ? detail::AsBase : detail::AsMember,
|
|
detail::StorageType = std::is_empty_v<B> &&
|
|
!std::is_base_of<A, B>::value &&
|
|
!std::is_base_of<B, A>::value
|
|
? detail::AsBase
|
|
: detail::AsMember>
|
|
struct CompactPairHelper;
|
|
|
|
template <typename A, typename B>
|
|
struct CompactPairHelper<A, B, AsMember, AsMember> {
|
|
protected:
|
|
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
|
|
std::size_t... BIndexes>
|
|
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
|
|
std::tuple<BArgs...>& aBTuple,
|
|
std::index_sequence<AIndexes...>,
|
|
std::index_sequence<BIndexes...>)
|
|
: mFirstA(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
|
|
mSecondB(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
|
|
|
|
public:
|
|
template <typename AArg, typename BArg>
|
|
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
|
|
: mFirstA(std::forward<AArg>(aA)), mSecondB(std::forward<BArg>(aB)) {}
|
|
|
|
constexpr A& first() { return mFirstA; }
|
|
constexpr const A& first() const { return mFirstA; }
|
|
constexpr B& second() { return mSecondB; }
|
|
constexpr const B& second() const { return mSecondB; }
|
|
|
|
void swap(CompactPairHelper& aOther) {
|
|
std::swap(mFirstA, aOther.mFirstA);
|
|
std::swap(mSecondB, aOther.mSecondB);
|
|
}
|
|
|
|
private:
|
|
A mFirstA;
|
|
B mSecondB;
|
|
};
|
|
|
|
template <typename A, typename B>
|
|
struct CompactPairHelper<A, B, AsMember, AsBase> : private B {
|
|
protected:
|
|
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
|
|
std::size_t... BIndexes>
|
|
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
|
|
std::tuple<BArgs...>& aBTuple,
|
|
std::index_sequence<AIndexes...>,
|
|
std::index_sequence<BIndexes...>)
|
|
: B(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...),
|
|
mFirstA(std::forward<AArgs>(std::get<AIndexes>(aATuple))...) {}
|
|
|
|
public:
|
|
template <typename AArg, typename BArg>
|
|
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
|
|
: B(std::forward<BArg>(aB)), mFirstA(std::forward<AArg>(aA)) {}
|
|
|
|
constexpr A& first() { return mFirstA; }
|
|
constexpr const A& first() const { return mFirstA; }
|
|
constexpr B& second() { return *this; }
|
|
constexpr const B& second() const { return *this; }
|
|
|
|
void swap(CompactPairHelper& aOther) {
|
|
std::swap(mFirstA, aOther.mFirstA);
|
|
std::swap(static_cast<B&>(*this), static_cast<B&>(aOther));
|
|
}
|
|
|
|
private:
|
|
A mFirstA;
|
|
};
|
|
|
|
template <typename A, typename B>
|
|
struct CompactPairHelper<A, B, AsBase, AsMember> : private A {
|
|
protected:
|
|
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
|
|
std::size_t... BIndexes>
|
|
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
|
|
std::tuple<BArgs...>& aBTuple,
|
|
std::index_sequence<AIndexes...>,
|
|
std::index_sequence<BIndexes...>)
|
|
: A(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
|
|
mSecondB(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
|
|
|
|
public:
|
|
template <typename AArg, typename BArg>
|
|
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
|
|
: A(std::forward<AArg>(aA)), mSecondB(std::forward<BArg>(aB)) {}
|
|
|
|
constexpr A& first() { return *this; }
|
|
constexpr const A& first() const { return *this; }
|
|
constexpr B& second() { return mSecondB; }
|
|
constexpr const B& second() const { return mSecondB; }
|
|
|
|
void swap(CompactPairHelper& aOther) {
|
|
std::swap(static_cast<A&>(*this), static_cast<A&>(aOther));
|
|
std::swap(mSecondB, aOther.mSecondB);
|
|
}
|
|
|
|
private:
|
|
B mSecondB;
|
|
};
|
|
|
|
template <typename A, typename B>
|
|
struct CompactPairHelper<A, B, AsBase, AsBase> : private A, private B {
|
|
protected:
|
|
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
|
|
std::size_t... BIndexes>
|
|
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
|
|
std::tuple<BArgs...>& aBTuple,
|
|
std::index_sequence<AIndexes...>,
|
|
std::index_sequence<BIndexes...>)
|
|
: A(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
|
|
B(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
|
|
|
|
public:
|
|
template <typename AArg, typename BArg>
|
|
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
|
|
: A(std::forward<AArg>(aA)), B(std::forward<BArg>(aB)) {}
|
|
|
|
constexpr A& first() { return static_cast<A&>(*this); }
|
|
constexpr const A& first() const { return static_cast<A&>(*this); }
|
|
constexpr B& second() { return static_cast<B&>(*this); }
|
|
constexpr const B& second() const { return static_cast<B&>(*this); }
|
|
|
|
void swap(CompactPairHelper& aOther) {
|
|
std::swap(static_cast<A&>(*this), static_cast<A&>(aOther));
|
|
std::swap(static_cast<B&>(*this), static_cast<B&>(aOther));
|
|
}
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
/**
|
|
* CompactPair is the logical concatenation of an instance of A with an instance
|
|
* B. Space is conserved when possible. Neither A nor B may be a final class.
|
|
*
|
|
* In general if space conservation is not critical is preferred to use
|
|
* std::pair.
|
|
*
|
|
* It's typically clearer to have individual A and B member fields. Except if
|
|
* you want the space-conserving qualities of CompactPair, you're probably
|
|
* better off not using this!
|
|
*
|
|
* No guarantees are provided about the memory layout of A and B, the order of
|
|
* initialization or destruction of A and B, and so on. (This is approximately
|
|
* required to optimize space usage.) The first/second names are merely
|
|
* conceptual!
|
|
*/
|
|
template <typename A, typename B>
|
|
struct CompactPair : private detail::CompactPairHelper<A, B> {
|
|
typedef typename detail::CompactPairHelper<A, B> Base;
|
|
|
|
using Base::Base;
|
|
|
|
template <typename... AArgs, typename... BArgs>
|
|
constexpr CompactPair(std::piecewise_construct_t, std::tuple<AArgs...> aFirst,
|
|
std::tuple<BArgs...> aSecond)
|
|
: Base(aFirst, aSecond, std::index_sequence_for<AArgs...>(),
|
|
std::index_sequence_for<BArgs...>()) {}
|
|
|
|
CompactPair(CompactPair&& aOther) = default;
|
|
CompactPair(const CompactPair& aOther) = default;
|
|
|
|
CompactPair& operator=(CompactPair&& aOther) = default;
|
|
CompactPair& operator=(const CompactPair& aOther) = default;
|
|
|
|
/** The A instance. */
|
|
using Base::first;
|
|
/** The B instance. */
|
|
using Base::second;
|
|
|
|
/** Swap this pair with another pair. */
|
|
void swap(CompactPair& aOther) { Base::swap(aOther); }
|
|
};
|
|
|
|
/**
|
|
* MakeCompactPair allows you to construct a CompactPair instance using type
|
|
* inference. A call like this:
|
|
*
|
|
* MakeCompactPair(Foo(), Bar())
|
|
*
|
|
* will return a CompactPair<Foo, Bar>.
|
|
*/
|
|
template <typename A, typename B>
|
|
CompactPair<std::remove_cv_t<std::remove_reference_t<A>>,
|
|
std::remove_cv_t<std::remove_reference_t<B>>>
|
|
MakeCompactPair(A&& aA, B&& aB) {
|
|
return CompactPair<std::remove_cv_t<std::remove_reference_t<A>>,
|
|
std::remove_cv_t<std::remove_reference_t<B>>>(
|
|
std::forward<A>(aA), std::forward<B>(aB));
|
|
}
|
|
|
|
/**
|
|
* CompactPair equality comparison
|
|
*/
|
|
template <typename A, typename B>
|
|
bool operator==(const CompactPair<A, B>& aLhs, const CompactPair<A, B>& aRhs) {
|
|
return aLhs.first() == aRhs.first() && aLhs.second() == aRhs.second();
|
|
}
|
|
|
|
} // namespace mozilla
|
|
|
|
namespace std {
|
|
|
|
template <typename A, class B>
|
|
void swap(mozilla::CompactPair<A, B>& aX, mozilla::CompactPair<A, B>& aY) {
|
|
aX.swap(aY);
|
|
}
|
|
|
|
} // namespace std
|
|
|
|
#endif /* mozilla_CompactPair_h */
|