mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-30 16:22:00 +00:00
145 lines
3.4 KiB
C++
145 lines
3.4 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/. */
|
|
|
|
#ifndef mozilla_MaybeOneOf_h
|
|
#define mozilla_MaybeOneOf_h
|
|
|
|
#include "mozilla/Alignment.h"
|
|
#include "mozilla/Assertions.h"
|
|
#include "mozilla/Move.h"
|
|
#include "mozilla/TemplateLib.h"
|
|
|
|
#include <new> // For placement new
|
|
|
|
namespace mozilla {
|
|
|
|
/*
|
|
* MaybeOneOf<T1, T2> is like Maybe, but it supports constructing either T1
|
|
* or T2. When a MaybeOneOf<T1, T2> is constructed, it is |empty()|, i.e.,
|
|
* no value has been constructed and no destructor will be called when the
|
|
* MaybeOneOf<T1, T2> is destroyed. Upon calling |construct<T1>()| or
|
|
* |construct<T2>()|, a T1 or T2 object will be constructed with the given
|
|
* arguments and that object will be destroyed when the owning MaybeOneOf is
|
|
* destroyed.
|
|
*/
|
|
template<class T1, class T2>
|
|
class MaybeOneOf
|
|
{
|
|
AlignedStorage<tl::Max<sizeof(T1), sizeof(T2)>::value> storage;
|
|
|
|
enum State { None, SomeT1, SomeT2 } state;
|
|
template <class T, class Ignored = void> struct Type2State {};
|
|
|
|
template <class T>
|
|
T& as()
|
|
{
|
|
MOZ_ASSERT(state == Type2State<T>::result);
|
|
return *(T*)storage.addr();
|
|
}
|
|
|
|
template <class T>
|
|
const T& as() const
|
|
{
|
|
MOZ_ASSERT(state == Type2State<T>::result);
|
|
return *(T*)storage.addr();
|
|
}
|
|
|
|
public:
|
|
MaybeOneOf() : state(None) {}
|
|
~MaybeOneOf() { destroyIfConstructed(); }
|
|
|
|
bool empty() const { return state == None; }
|
|
|
|
template <class T>
|
|
bool constructed() const { return state == Type2State<T>::result; }
|
|
|
|
template <class T>
|
|
void construct()
|
|
{
|
|
MOZ_ASSERT(state == None);
|
|
state = Type2State<T>::result;
|
|
::new (storage.addr()) T();
|
|
}
|
|
|
|
template <class T, class U>
|
|
void construct(U&& aU)
|
|
{
|
|
MOZ_ASSERT(state == None);
|
|
state = Type2State<T>::result;
|
|
::new (storage.addr()) T(Move(aU));
|
|
}
|
|
|
|
template <class T, class U1>
|
|
void construct(const U1& aU1)
|
|
{
|
|
MOZ_ASSERT(state == None);
|
|
state = Type2State<T>::result;
|
|
::new (storage.addr()) T(aU1);
|
|
}
|
|
|
|
template <class T, class U1, class U2>
|
|
void construct(const U1& aU1, const U2& aU2)
|
|
{
|
|
MOZ_ASSERT(state == None);
|
|
state = Type2State<T>::result;
|
|
::new (storage.addr()) T(aU1, aU2);
|
|
}
|
|
|
|
template <class T>
|
|
T& ref()
|
|
{
|
|
return as<T>();
|
|
}
|
|
|
|
template <class T>
|
|
const T& ref() const
|
|
{
|
|
return as<T>();
|
|
}
|
|
|
|
void destroy()
|
|
{
|
|
MOZ_ASSERT(state == SomeT1 || state == SomeT2);
|
|
if (state == SomeT1) {
|
|
as<T1>().~T1();
|
|
} else if (state == SomeT2) {
|
|
as<T2>().~T2();
|
|
}
|
|
state = None;
|
|
}
|
|
|
|
void destroyIfConstructed()
|
|
{
|
|
if (!empty()) {
|
|
destroy();
|
|
}
|
|
}
|
|
|
|
private:
|
|
MaybeOneOf(const MaybeOneOf& aOther) MOZ_DELETE;
|
|
const MaybeOneOf& operator=(const MaybeOneOf& aOther) MOZ_DELETE;
|
|
};
|
|
|
|
template <class T1, class T2>
|
|
template <class Ignored>
|
|
struct MaybeOneOf<T1, T2>::Type2State<T1, Ignored>
|
|
{
|
|
typedef MaybeOneOf<T1, T2> Enclosing;
|
|
static const typename Enclosing::State result = Enclosing::SomeT1;
|
|
};
|
|
|
|
template <class T1, class T2>
|
|
template <class Ignored>
|
|
struct MaybeOneOf<T1, T2>::Type2State<T2, Ignored>
|
|
{
|
|
typedef MaybeOneOf<T1, T2> Enclosing;
|
|
static const typename Enclosing::State result = Enclosing::SomeT2;
|
|
};
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif /* mozilla_MaybeOneOf_h */
|