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