mirror of
https://github.com/classilla/tenfourfox.git
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172 lines
5.9 KiB
C++
172 lines
5.9 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 type-erased callable wrapper. */
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#ifndef mozilla_Function_h
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#define mozilla_Function_h
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#include "mozilla/Attributes.h" // for MOZ_IMPLICIT
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#include "mozilla/Move.h"
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#include "mozilla/UniquePtr.h"
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// |Function<Signature>| is a wrapper that can hold any type of callable
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// object that can be invoked in a way that's compatible with |Signature|.
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// The standard "type erasure" technique is used to avoid the type of the
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// wrapper depending on the concrete type of the wrapped callable.
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//
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// Supported callable types include non-member functions, static member
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// functions, and function objects (that is to say, objects with an overloaded
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// call operator; this includes C++11 lambdas). Member functions aren't
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// directly supported; they first need to be wrapped into a function object
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// using |std::mem_fn()| or an equivalent.
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//
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// |Signature| is a type of the form |ReturnType(Arguments...)|. Syntactically,
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// this is a function type; it's not used in any way other than serving as a
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// vehicle to encode the return and argument types into a single type.
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//
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// |Function| is default-constructible. A default-constructed instance is
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// considered "empty". Invoking an empty instance is undefined behaviour.
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// An empty instance can be populated with a callable by assigning to it.
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//
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// This class is intended to provide functionality similar to the C++11
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// standard library class |std::function|.
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namespace mozilla {
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namespace detail {
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template<typename ReturnType, typename... Arguments>
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class FunctionImplBase
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{
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public:
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virtual ~FunctionImplBase() {}
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virtual ReturnType call(Arguments... aArguments) = 0;
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};
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// Normal Callable Object.
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template <typename Callable, typename ReturnType, typename... Arguments>
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class FunctionImpl : public FunctionImplBase<ReturnType, Arguments...>
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{
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public:
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explicit FunctionImpl(const Callable& aCallable)
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: mCallable(aCallable) {}
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ReturnType call(Arguments... aArguments) override
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{
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return mCallable(Forward<Arguments>(aArguments)...);
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}
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private:
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Callable mCallable;
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};
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// Base class for passing pointer to member function.
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template <typename Callable, typename ReturnType, typename... Arguments>
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class MemberFunctionImplBase : public FunctionImplBase<ReturnType, Arguments...>
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{
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public:
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explicit MemberFunctionImplBase(const Callable& aCallable)
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: mCallable(aCallable) {}
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ReturnType call(Arguments... aArguments) override
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{
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return callInternal(Forward<Arguments>(aArguments)...);
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}
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private:
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template<typename ThisType, typename... Args>
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ReturnType callInternal(ThisType* aThis, Args&&... aArguments)
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{
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return (aThis->*mCallable)(Forward<Args>(aArguments)...);
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}
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template<typename ThisType, typename... Args>
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ReturnType callInternal(ThisType&& aThis, Args&&... aArguments)
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{
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return (aThis.*mCallable)(Forward<Args>(aArguments)...);
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}
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Callable mCallable;
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};
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// For non-const member function specialization of FunctionImpl.
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template <typename ThisType, typename... Args, typename ReturnType, typename... Arguments>
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class FunctionImpl<ReturnType(ThisType::*)(Args...),
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ReturnType, Arguments...>
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: public MemberFunctionImplBase<ReturnType(ThisType::*)(Args...),
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ReturnType, Arguments...>
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{
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public:
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explicit FunctionImpl(ReturnType(ThisType::*aMemberFunc)(Args...))
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: MemberFunctionImplBase<ReturnType(ThisType::*)(Args...),
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ReturnType, Arguments...>(aMemberFunc)
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{}
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};
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// For const member function specialization of FunctionImpl.
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template <typename ThisType, typename... Args, typename ReturnType, typename... Arguments>
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class FunctionImpl<ReturnType(ThisType::*)(Args...) const,
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ReturnType, Arguments...>
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: public MemberFunctionImplBase<ReturnType(ThisType::*)(Args...) const,
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ReturnType, Arguments...>
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{
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public:
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explicit FunctionImpl(ReturnType(ThisType::*aConstMemberFunc)(Args...) const)
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: MemberFunctionImplBase<ReturnType(ThisType::*)(Args...) const,
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ReturnType, Arguments...>(aConstMemberFunc)
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{}
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};
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} // namespace detail
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// The primary template is never defined. As |Signature| is required to be
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// of the form |ReturnType(Arguments...)|, we only define a partial
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// specialization that matches this form. This allows us to use |ReturnType|
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// and |Arguments| in the definition of the specialization without having to
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// introspect |Signature|.
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template<typename Signature>
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class Function;
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template<typename ReturnType, typename... Arguments>
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class Function<ReturnType(Arguments...)>
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{
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public:
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Function() {}
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// This constructor is implicit to match the interface of |std::function|.
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template <typename Callable>
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MOZ_IMPLICIT Function(const Callable& aCallable)
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: mImpl(MakeUnique<detail::FunctionImpl<Callable, ReturnType, Arguments...>>(aCallable))
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{}
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// Move constructor and move assingment operator.
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// These should be generated automatically, but MSVC doesn't do that yet.
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Function(Function&& aOther) : mImpl(Move(aOther.mImpl)) {}
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Function& operator=(Function&& aOther) {
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mImpl = Move(aOther.mImpl);
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return *this;
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}
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template <typename Callable>
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Function& operator=(const Callable& aCallable)
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{
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mImpl = MakeUnique<detail::FunctionImpl<Callable, ReturnType, Arguments...>>(aCallable);
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return *this;
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}
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template<typename... Args>
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ReturnType operator()(Args&&... aArguments) const
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{
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MOZ_ASSERT(mImpl);
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return mImpl->call(Forward<Args>(aArguments)...);
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}
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private:
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// TODO: Consider implementing a small object optimization.
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UniquePtr<detail::FunctionImplBase<ReturnType, Arguments...>> mImpl;
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};
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} // namespace mozilla
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#endif /* mozilla_Function_h */
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