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$$ This is a pump file for generating file templates. Pump is a python
$$ script that is part of the Google Test suite of utilities. Description
$$ can be found here:
$$ MAX_ARITY controls the number of arguments that Bind() supports.
$$ The amount of code, and more importantly, the number of template types
$$ generated by pump grows at O(MAX_ARITY^2).
$$ We tried going to 11 and found it imposed an extra 10 penalty on windows
$$ cycle times compared to our original baseline of 6.
$$ Currently 7 is chosen as a compromise between supporting a convenient
$$ number of arguments and keeping compile times low. At 7, we have 115
$$ templates being generated by pump.
$$ Be careful when adjusting this number. If people find a need to bind
$$ a larger number of arguments, consider refactoring the function to use
$$ a param struct instead of raising the MAX_ARITY.
$$ See for more context.
$var MAX_ARITY = 7
// 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.
// 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 COMPILE_ASSERT asserts 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 {
$for ARITY [[
$range ARG 1..ARITY
template <typename Functor[[]]
$if ARITY > 0 [[, ]] $for ARG , [[typename P$(ARG)]]>
typename internal::BindState<
typename internal::FunctorTraits<Functor>::RunnableType,
typename internal::FunctorTraits<Functor>::RunType,
void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])>
Bind(Functor functor
$if ARITY > 0 [[, ]] $for ARG , [[const P$(ARG)& p$(ARG)]]) {
// Typedefs for how to store and run the functor.
typedef typename internal::FunctorTraits<Functor>::RunnableType RunnableType;
typedef typename internal::FunctorTraits<Functor>::RunType RunType;
$if ARITY > 0 [[
// 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 internal::FunctionTraits<typename RunnableType::RunType>
// 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.
!($for ARG || [[
is_non_const_reference<typename BoundFunctorTraits::A$(ARG)Type>::value ]]),
$for ARG [[
$if ARG == 1 [[
// 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.
internal::HasIsMethodTag<RunnableType>::value ||
COMPILE_ASSERT(!internal::HasIsMethodTag<RunnableType>::value ||
]] $else [[
]] $$ $if ARG
]] $$ $for ARG
typedef internal::BindState<RunnableType, RunType, [[]]
void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])> [[]]
return Callback<typename BindState::UnboundRunType>(
new BindState(internal::MakeRunnable(functor)[[]]
$if ARITY > 0 [[, ]] $for ARG , [[p$(ARG)]]));
]] $$ for ARITY
} // namespace base
#endif // BASE_BIND_H_