Support binding WeakPtr<> to methods with void return types.

base/bind_internal.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
 $$
 $$ http://code.google.com/p/googletest/wiki/PumpManual
 $$
 
 $var MAX_ARITY = 6
 
 // 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_INTERNAL_H_
 #define BASE_BIND_INTERNAL_H_
 #pragma once
 
 #include "base/bind_helpers.h"
 #include "base/callback_internal.h"
+#include "base/memory/weak_ptr.h"
 #include "base/template_util.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include "base/bind_internal_win.h"
 #endif
 
 namespace base {
 namespace internal {
 
 // The method by which a function is invoked is determined by 3 different
 // dimensions:
 //
 //   1) The type of function (normal or method).
 //   2) The arity of the function.
 //   3) The number of bound parameters.
 //
 // The templates below handle the determination of each of these dimensions.
 // In brief:
 //
 //   FunctionTraits<> -- Provides a normalied signature, and other traits.
 //   InvokerN<> -- Provides a DoInvoke() function that actually executes
 //                 a calback.
 //   InvokerStorageN<> -- Provides storage for the bound parameters, and
 //                        typedefs to the above.
+//   IsWeakMethod<> -- Determines if we are binding a method to a WeakPtr<>.
 //
 // More details about the design of each class is included in a comment closer
 // to their defition.
 
+
+// IsWeakMethod determines if we are binding a method to a WeakPtr<> for an
+// object.  It is used to select an InvokerN that will no-op itself in the
+// event the WeakPtr<> for the target object is invalidated.
+template <bool IsMethod, typename T>
+struct IsWeakMethod : public false_type {};
+
+template <typename T>
+struct IsWeakMethod<true, WeakPtr<T> > : public true_type {};
+
 // FunctionTraits<>
 //
 // The FunctionTraits<> template determines the type of function, and also
 // creates a NormalizedType used to select the InvokerN classes.  It turns out
 // that syntactically, you only really have 2 variations when invoking a
 // funciton pointer: normal, and method.  One is invoked func_ptr(arg1). The
 // other is invoked (*obj_->method_ptr(arg1)).
 //
 // However, in the type system, there are many more distinctions. In standard
 // C++, there's all variations of const, and volatile on the function pointer.
@@ skipping 17 matching lines @@
 $for ARITY [[
 $range ARG 1..ARITY
 
 // Function: Arity $(ARITY).
 template <typename R[[]]
 $if ARITY > 0[[, ]] $for ARG , [[typename X$(ARG)]]>
 struct FunctionTraits<R(*)($for ARG , [[X$(ARG)]])> {
   typedef R (*NormalizedSig)($for ARG , [[X$(ARG)]]);
   typedef false_type IsMethod;
 
+  typedef R Return;
+
 $if ARITY > 0 [[
 
   // Target type for each bound parameter.
 
 $for ARG [[
   typedef X$(ARG) B$(ARG);
 
 ]]  $$ for ARG
 ]]  $$ if ARITY > 0
 
 };
 
 // Method: Arity $(ARITY).
 template <typename R, typename T[[]]
 $if ARITY > 0[[, ]] $for ARG , [[typename X$(ARG)]]>
 struct FunctionTraits<R(T::*)($for ARG , [[X$(ARG)]])> {
   typedef R (T::*NormalizedSig)($for ARG , [[X$(ARG)]]);
   typedef true_type IsMethod;
 
+  typedef R Return;
+
   // Target type for each bound parameter.
   typedef T B1;
 
 $for ARG [[
   typedef X$(ARG) B$(ARG + 1);
 
 ]]  $$ for ARG
 
 };
 
 // Const Method: Arity $(ARITY).
 template <typename R, typename T[[]]
 $if ARITY > 0[[, ]] $for ARG , [[typename X$(ARG)]]>
 struct FunctionTraits<R(T::*)($for ARG , [[X$(ARG)]]) const> {
   typedef R (T::*NormalizedSig)($for ARG , [[X$(ARG)]]);
   typedef true_type IsMethod;
 
+  typedef R Return;
+
   // Target type for each bound parameter.
   typedef T B1;
 
 $for ARG [[
   typedef X$(ARG) B$(ARG + 1);
 
 ]]  $$ for ARG
 
 };
 
@@ skipping 15 matching lines @@
 // safe.
 //
 // The InvokerN templates are the only point that knows the number of bound
 // and unbound arguments.  This is intentional because it allows the other
 // templates classes in the system to only have as many specializations as
 // the max arity of function we wish to support.
 
 $range BOUND 0..MAX_ARITY
 $for BOUND [[
 
-template <typename StorageType, typename NormalizedSig>
+template <bool IsWeak, typename StorageType, typename NormalizedSig>
 struct Invoker$(BOUND);
 
 $range ARITY 0..MAX_ARITY
 $for ARITY [[
 
 $var UNBOUND = ARITY - BOUND
 $if UNBOUND >= 0 [[
 
 $$ Variables for function traits generation.
 $range ARG 1..ARITY
 $range BOUND_ARG 1..BOUND
 $range UNBOUND_ARG (ARITY - UNBOUND + 1)..ARITY
 
 $$ Variables for method traits generation. We are always short one arity since
 $$ the first bound parameter is the object.
 $var M_ARITY = ARITY - 1
 $range M_ARG 1..M_ARITY
 $range M_BOUND_ARG 2..BOUND
 $range M_UNBOUND_ARG (M_ARITY - UNBOUND + 1)..M_ARITY
 
 // Function: Arity $(ARITY) -> $(UNBOUND).
 template <typename StorageType, typename R[[]]
 $if ARITY > 0 [[,]][[]]
 $for ARG , [[typename X$(ARG)]]>
-struct Invoker$(BOUND)<StorageType, R(*)($for ARG , [[X$(ARG)]])> {
+struct Invoker$(BOUND)<false, StorageType, R(*)($for ARG , [[X$(ARG)]])> {
   static R DoInvoke(InvokerStorageBase* base[[]]
 $if UNBOUND != 0 [[, ]][[]]
 $for UNBOUND_ARG , [[typename internal::ParamTraits<X$(UNBOUND_ARG)>::ForwardType x$(UNBOUND_ARG)]]) {
     StorageType* invoker = static_cast<StorageType*>(base);
     return invoker->f_($for BOUND_ARG , [[Unwrap(invoker->p$(BOUND_ARG)_)]][[]]
 $$ Add comma if there are both boudn and unbound args.
 $if UNBOUND > 0 [[$if BOUND > 0 [[, ]]]][[]]
 $for UNBOUND_ARG , [[x$(UNBOUND_ARG)]]);
   }
 };
 
 $if BOUND > 0 [[
 
 // Method: Arity $(M_ARITY) -> $(UNBOUND).
 template <typename StorageType, typename R, typename T[[]]
 $if M_ARITY > 0[[, ]] $for M_ARG , [[typename X$(M_ARG)]]>
-struct Invoker$(BOUND)<StorageType, R(T::*)($for M_ARG , [[X$(M_ARG)]])> {
+struct Invoker$(BOUND)<false, StorageType, R(T::*)($for M_ARG , [[X$(M_ARG)]])> {
   static R DoInvoke(InvokerStorageBase* base[[]]
 $if UNBOUND > 0 [[, ]][[]]
 $for M_UNBOUND_ARG , [[typename internal::ParamTraits<X$(M_UNBOUND_ARG)>::ForwardType x$(M_UNBOUND_ARG)]]) {
     StorageType* invoker = static_cast<StorageType*>(base);
     return (Unwrap(invoker->p1_)->*invoker->f_)([[]]
 $for M_BOUND_ARG , [[Unwrap(invoker->p$(M_BOUND_ARG)_)]][[]]
 $if UNBOUND > 0 [[$if BOUND > 1 [[, ]]]][[]]
 $for M_UNBOUND_ARG , [[x$(M_UNBOUND_ARG)]]);
   }
 };
 
+// WeakPtr Method: Arity $(M_ARITY) -> $(UNBOUND).
+template <typename StorageType, typename T[[]]
+$if M_ARITY > 0[[, ]] $for M_ARG , [[typename X$(M_ARG)]]>
+struct Invoker$(BOUND)<true, StorageType, void(T::*)($for M_ARG , [[X$(M_ARG)]])> {
+  static void DoInvoke(InvokerStorageBase* base[[]]
+$if UNBOUND > 0 [[, ]][[]]
+$for M_UNBOUND_ARG , [[typename internal::ParamTraits<X$(M_UNBOUND_ARG)>::ForwardType x$(M_UNBOUND_ARG)]]) {
+    StorageType* invoker = static_cast<StorageType*>(base);
+    typename StorageType::P1Traits::StorageType& weak_ptr = invoker->p1_;
+    if (!weak_ptr.get()) {
+      return;
+    }
+    (weak_ptr->*invoker->f_)([[]]
+$for M_BOUND_ARG , [[Unwrap(invoker->p$(M_BOUND_ARG)_)]][[]]
+$if UNBOUND > 0 [[$if BOUND > 1 [[, ]]]][[]]
+$for M_UNBOUND_ARG , [[x$(M_UNBOUND_ARG)]]);
+  }
+};
+
 ]]  $$ if BOUND
 
 ]]  $$ if UNBOUND
 ]]  $$ for ARITY
 ]]  $$ for BOUND
 
-
 // InvokerStorageN<>
 //
 // These are the actual storage classes for the Invokers.
 //
 // Though these types are "classes", they are being used as structs with
 // all member variable public.  We cannot make it a struct because it inherits
 // from a class which causes a compiler warning.  We cannot add a "Run()" method
 // that forwards the unbound arguments because that would require we unwrap the
 // Sig type like in InvokerN above to know the return type, and the arity
 // of Run().
 //
 // An alternate solution would be to merge InvokerN and InvokerStorageN,
 // but the generated code seemed harder to read.
 
 $for BOUND [[
 $range BOUND_ARG 1..BOUND
 
 template <typename Sig[[]]
 $if BOUND > 0 [[, ]]
 $for BOUND_ARG , [[typename P$(BOUND_ARG)]]>
 class InvokerStorage$(BOUND) : public InvokerStorageBase {
  public:
   typedef InvokerStorage$(BOUND) StorageType;
   typedef FunctionTraits<Sig> TargetTraits;
-  typedef Invoker$(BOUND)<StorageType, typename TargetTraits::NormalizedSig> Invoker;
   typedef typename TargetTraits::IsMethod IsMethod;
+  typedef Sig Signature;
+
+$for BOUND_ARG [[
+  typedef ParamTraits<P$(BOUND_ARG)> P$(BOUND_ARG)Traits;
+
+]]
+
+$if BOUND == 0 [[
+  typedef Invoker$(BOUND)<false, StorageType,
+                   typename TargetTraits::NormalizedSig> Invoker;
+]] $else [[
+  typedef Invoker$(BOUND)<IsWeakMethod<IsMethod::value, P1>::value, StorageType,
+                   typename TargetTraits::NormalizedSig> Invoker;
+  COMPILE_ASSERT(!(IsWeakMethod<IsMethod::value, P1>::value) ||
+                 is_void<typename TargetTraits::Return>::value,
+                 weak_ptrs_can_only_bind_to_methods_without_return_values);
+]]
+
 
 $for BOUND_ARG [[
 $if BOUND_ARG == 1 [[
 
   // For methods, we need to be careful for parameter 1.  We skip the
   // scoped_refptr check because the binder itself takes care of this. We also
   // disallow binding of an array as the method's target object.
   COMPILE_ASSERT(IsMethod::value ||
                  !internal::UnsafeBindtoRefCountedArg<P$(BOUND_ARG)>::value,
                  p$(BOUND_ARG)_is_refcounted_type_and_needs_scoped_refptr);
@@ skipping 50 matching lines @@
 
 ]]
 };
 
 ]]  $$ for BOUND
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_BIND_INTERNAL_H_