101 lines
4.3 KiB
C++
101 lines
4.3 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_BIND_H_
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#define BASE_BIND_H_
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#include "base/bind_internal.h"
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#include "base/callback_internal.h"
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// -----------------------------------------------------------------------------
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// Usage documentation
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// -----------------------------------------------------------------------------
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//
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// See base/callback.h for documentation.
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//
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//
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// -----------------------------------------------------------------------------
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// Implementation notes
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// -----------------------------------------------------------------------------
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//
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// If you're reading the implementation, before proceeding further, you should
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// read the top comment of base/bind_internal.h for a definition of common
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// terms and concepts.
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//
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// RETURN TYPES
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//
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// Though Bind()'s result is meant to be stored in a Callback<> type, it
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// cannot actually return the exact type without requiring a large amount
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// of extra template specializations. The problem is that in order to
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// discern the correct specialization of Callback<>, Bind would need to
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// unwrap the function signature to determine the signature's arity, and
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// whether or not it is a method.
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//
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// Each unique combination of (arity, function_type, num_prebound) where
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// function_type is one of {function, method, const_method} would require
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// one specialization. We eventually have to do a similar number of
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// specializations anyways in the implementation (see the Invoker<>,
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// classes). However, it is avoidable in Bind if we return the result
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// via an indirection like we do below.
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//
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// TODO(ajwong): We might be able to avoid this now, but need to test.
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//
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// It is possible to move most of the static_assert into BindState<>, but it
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// feels a little nicer to have the asserts here so people do not need to crack
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// open bind_internal.h. On the other hand, it makes Bind() harder to read.
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namespace base {
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template <typename Functor, typename... Args>
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base::Callback<
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typename internal::BindState<
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typename internal::FunctorTraits<Functor>::RunnableType,
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typename internal::FunctorTraits<Functor>::RunType,
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typename internal::CallbackParamTraits<Args>::StorageType...>
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::UnboundRunType>
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Bind(Functor functor, const Args&... args) {
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// Type aliases for how to store and run the functor.
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using RunnableType = typename internal::FunctorTraits<Functor>::RunnableType;
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using RunType = typename internal::FunctorTraits<Functor>::RunType;
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// Use RunnableType::RunType instead of RunType above because our
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// checks below for bound references need to know what the actual
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// functor is going to interpret the argument as.
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using BoundRunType = typename RunnableType::RunType;
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using BoundArgs =
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internal::TakeTypeListItem<sizeof...(Args),
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internal::ExtractArgs<BoundRunType>>;
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// Do not allow binding a non-const reference parameter. Non-const reference
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// parameters are disallowed by the Google style guide. Also, binding a
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// non-const reference parameter can make for subtle bugs because the
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// invoked function will receive a reference to the stored copy of the
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// argument and not the original.
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static_assert(!internal::HasNonConstReferenceItem<BoundArgs>::value,
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"do not bind functions with nonconst ref");
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const bool is_method = internal::HasIsMethodTag<RunnableType>::value;
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// For methods, we need to be careful for parameter 1. We do not require
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// a scoped_refptr because BindState<> itself takes care of AddRef() for
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// methods. We also disallow binding of an array as the method's target
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// object.
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static_assert(!internal::BindsArrayToFirstArg<is_method, Args...>::value,
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"first bound argument to method cannot be array");
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static_assert(
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!internal::HasRefCountedParamAsRawPtr<is_method, Args...>::value,
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"a parameter is a refcounted type and needs scoped_refptr");
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using BindState = internal::BindState<
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RunnableType, RunType,
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typename internal::CallbackParamTraits<Args>::StorageType...>;
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return Callback<typename BindState::UnboundRunType>(
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new BindState(internal::MakeRunnable(functor), args...));
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}
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} // namespace base
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#endif // BASE_BIND_H_
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