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/*
* Copyright (C) 2015-2016 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <wtf/ForbidHeapAllocation.h>
namespace WTF {
// You can use ScopedLambda to efficiently pass lambdas without allocating memory or requiring
// template specialization of the callee. The callee should be declared as:
//
// void foo(const ScopedLambda<MyThings* (int, Stuff&)>&);
//
// The caller just does:
//
// void foo(scopedLambda<MyThings* (int, Stuff&)>([&] (int x, Stuff& y) -> MyThings* { blah }));
//
// Note that this relies on foo() not escaping the lambda. The lambda is only valid while foo() is
// on the stack - hence the name ScopedLambda.
template<typename FunctionType> class ScopedLambda;
template<typename ResultType, typename... ArgumentTypes>
class ScopedLambda<ResultType (ArgumentTypes...)> {
WTF_FORBID_HEAP_ALLOCATION;
public:
ScopedLambda(ResultType (*impl)(void* arg, ArgumentTypes...) = nullptr, void* arg = nullptr)
: m_impl(impl)
, m_arg(arg)
{
}
template<typename... PassedArgumentTypes>
ResultType operator()(PassedArgumentTypes&&... arguments) const
{
return m_impl(m_arg, std::forward<PassedArgumentTypes>(arguments)...);
}
private:
ResultType (*m_impl)(void* arg, ArgumentTypes...);
void *m_arg;
};
template<typename FunctionType, typename Functor> class ScopedLambdaFunctor;
template<typename ResultType, typename... ArgumentTypes, typename Functor>
class ScopedLambdaFunctor<ResultType (ArgumentTypes...), Functor> : public ScopedLambda<ResultType (ArgumentTypes...)> {
public:
template<typename PassedFunctor>
ScopedLambdaFunctor(PassedFunctor&& functor)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(std::forward<PassedFunctor>(functor))
{
}
// We need to make sure that copying and moving ScopedLambdaFunctor results in a ScopedLambdaFunctor
// whose ScopedLambda supertype still points to this rather than other.
ScopedLambdaFunctor(const ScopedLambdaFunctor& other)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(other.m_functor)
{
}
ScopedLambdaFunctor(ScopedLambdaFunctor&& other)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(WTFMove(other.m_functor))
{
}
ScopedLambdaFunctor& operator=(const ScopedLambdaFunctor& other)
{
m_functor = other.m_functor;
return *this;
}
ScopedLambdaFunctor& operator=(ScopedLambdaFunctor&& other)
{
m_functor = WTFMove(other.m_functor);
return *this;
}
private:
static ResultType implFunction(void* argument, ArgumentTypes... arguments)
{
return static_cast<ScopedLambdaFunctor*>(argument)->m_functor(arguments...);
}
Functor m_functor;
};
// Can't simply rely on perfect forwarding because then the ScopedLambdaFunctor would point to the functor
// by const reference. This would be surprising in situations like:
//
// auto scopedLambda = scopedLambda<Foo(Bar)>([&] (Bar) -> Foo { ... });
//
// We expected scopedLambda to be valid for its entire lifetime, but if it computed the lambda by reference
// then it would be immediately invalid.
template<typename FunctionType, typename Functor>
ScopedLambdaFunctor<FunctionType, Functor> scopedLambda(const Functor& functor)
{
return ScopedLambdaFunctor<FunctionType, Functor>(functor);
}
template<typename FunctionType, typename Functor>
ScopedLambdaFunctor<FunctionType, Functor> scopedLambda(Functor&& functor)
{
return ScopedLambdaFunctor<FunctionType, Functor>(std::forward<Functor>(functor));
}
template<typename FunctionType, typename Functor> class ScopedLambdaRefFunctor;
template<typename ResultType, typename... ArgumentTypes, typename Functor>
class ScopedLambdaRefFunctor<ResultType (ArgumentTypes...), Functor> : public ScopedLambda<ResultType (ArgumentTypes...)> {
public:
ScopedLambdaRefFunctor(const Functor& functor)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(&functor)
{
}
// We need to make sure that copying and moving ScopedLambdaRefFunctor results in a
// ScopedLambdaRefFunctor whose ScopedLambda supertype still points to this rather than
// other.
ScopedLambdaRefFunctor(const ScopedLambdaRefFunctor& other)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(other.m_functor)
{
}
ScopedLambdaRefFunctor(ScopedLambdaRefFunctor&& other)
: ScopedLambda<ResultType (ArgumentTypes...)>(implFunction, this)
, m_functor(other.m_functor)
{
}
ScopedLambdaRefFunctor& operator=(const ScopedLambdaRefFunctor& other)
{
m_functor = other.m_functor;
return *this;
}
ScopedLambdaRefFunctor& operator=(ScopedLambdaRefFunctor&& other)
{
m_functor = other.m_functor;
return *this;
}
private:
static ResultType implFunction(void* argument, ArgumentTypes... arguments)
{
return (*static_cast<ScopedLambdaRefFunctor*>(argument)->m_functor)(arguments...);
}
const Functor* m_functor;
};
// This is for when you already refer to a functor by reference, and you know its lifetime is
// good. This just creates a ScopedLambda that points to your functor.
//
// Note that this is always wrong:
//
// auto ref = scopedLambdaRef([...] (...) {...});
//
// Because the scopedLambdaRef will refer to the lambda by reference, and the lambda will die after the
// semicolon. Use scopedLambda() in that case.
template<typename FunctionType, typename Functor>
ScopedLambdaRefFunctor<FunctionType, Functor> scopedLambdaRef(const Functor& functor)
{
return ScopedLambdaRefFunctor<FunctionType, Functor>(functor);
}
} // namespace WTF
using WTF::ScopedLambda;
using WTF::scopedLambda;
using WTF::scopedLambdaRef;
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