Callback API Change: Reimplement Bind(); support IgnoreResult, full currying, and use less types

base/callback.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:
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 $var MAX_ARITY = 6
 
 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
@@ skipping 111 matching lines @@
 // HOW THE IMPLEMENTATION WORKS:
 //
 // There are three main components to the system:
 //   1) The Callback classes.
 //   2) The Bind() functions.
 //   3) The arguments wrappers (eg., Unretained() and ConstRef()).
 //
 // The Callback classes represent a generic function pointer. Internally,
 // it stores a refcounted piece of state that represents the target function
 // and all its bound parameters.  Each Callback specialization has a templated
-// constructor that takes an InvokerStorageHolder<> object.  In the context of
-// the constructor, the static type of this InvokerStorageHolder<> object
+// constructor that takes an BindStateHolder<> object.  In the context of
+// the constructor, the static type of this BindStateHolder<> object
 // uniquely identifies the function it is representing, all its bound
 // parameters, and a DoInvoke() that is capable of invoking the target.
 //
-// Callback's constructor is takes the InvokerStorageHolder<> that has the
+// Callback's constructor is takes the BindStateHolder<> that has the
 // full static type and erases the target function type, and the bound
 // parameters.  It does this by storing a pointer to the specific DoInvoke()
-// function, and upcasting the state of InvokerStorageHolder<> to a
-// InvokerStorageBase. This is safe as long as this InvokerStorageBase pointer
+// function, and upcasting the state of BindStateHolder<> to a
+// BindStateBase. This is safe as long as this BindStateBase pointer
 // is only used with the stored DoInvoke() pointer.
 //
-// To create InvokerStorageHolder<> objects, we use the Bind() functions.
+// To create BindStateHolder<> objects, we use the Bind() functions.
 // These functions, along with a set of internal templates, are reponsible for
 //
 //  - Unwrapping the function signature into return type, and parameters
 //  - Determining the number of parameters that are bound
 //  - Creating the storage for the bound parameters
 //  - Performing compile-time asserts to avoid error-prone behavior
-//  - Returning an InvokerStorageHolder<> with an DoInvoke() that has an arity
+//  - Returning an BindStateHolder<> with an DoInvoke() that has an arity
 //    matching the number of unbound parameters, and knows the correct
 //    refcounting semantics for the target object if we are binding a class
 //    method.
 //
 // The Bind functions do the above using type-inference, and template
 // specializations.
 //
 // By default Bind() will store copies of all bound parameters, and attempt
 // to refcount a target object if the function being bound is a class method.
 //
@@ skipping 81 matching lines @@
 
 $if ARITY == 0 [[
 template <typename R>
 class Callback<R(void)> : public internal::CallbackBase {
 ]] $else [[
 template <typename R, $for ARG , [[typename A$(ARG)]]>
 class Callback<R($for ARG , [[A$(ARG)]])> : public internal::CallbackBase {
 ]]
 
  public:
-  typedef R(*PolymorphicInvoke)(
-      internal::InvokerStorageBase*[[]]
-$if ARITY != 0 [[, ]]
-$for ARG , [[typename internal::ParamTraits<A$(ARG)>::ForwardType]]);
+  typedef R(RunType)($for ARG , [[A$(ARG)]]);
 
   Callback() : CallbackBase(NULL, NULL) { }
 
-  // We pass InvokerStorageHolder by const ref to avoid incurring an
+  // We pass BindStateHolder by const ref to avoid incurring an
   // unnecessary AddRef/Unref pair even though we will modify the object.
   // We cannot use a normal reference because the compiler will warn
   // since this is often used on a return value, which is a temporary.
   //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
   template <typename T>
-  Callback(const internal::InvokerStorageHolder<T>& invoker_holder)
-      : CallbackBase(
-          reinterpret_cast<InvokeFuncStorage>(&T::Invoker::DoInvoke),
-          &invoker_holder.invoker_storage_) {
-    COMPILE_ASSERT((is_same<PolymorphicInvoke,
-                    typename T::Invoker::DoInvokeType>::value),
-                   callback_type_does_not_match_bind_result);
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
+    // so the compiler will typecheck that the passed in Run() method has
+    // the correct type.
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
+    polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
   bool Equals(const Callback& other) const {
     return CallbackBase::Equals(other);
   }
 
   R Run($for ARG ,
-        [[typename internal::ParamTraits<A$(ARG)>::ForwardType a$(ARG)]]) const {
+        [[typename internal::CallbackParamTraits<A$(ARG)>::ForwardType a$(ARG)]]) const {
     PolymorphicInvoke f =
         reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
 
-    return f(invoker_storage_.get()[[]]
+    return f(bind_state_.get()[[]]
 $if ARITY != 0 [[, ]]
 $for ARG ,
              [[a$(ARG)]]);
   }
+
+ private:
+  typedef R(*PolymorphicInvoke)(
+      internal::BindStateBase*[[]]
+$if ARITY != 0 [[, ]]
+$for ARG , [[typename internal::CallbackParamTraits<A$(ARG)>::ForwardType]]);
+
 };
 
 
 ]]  $$ for ARITY
 
 // Syntactic sugar to make Callbacks<void(void)> easier to declare since it
 // will be used in a lot of APIs with delayed execution.
 typedef Callback<void(void)> Closure;
 
 }  // namespace base
 
 #endif  // BASE_CALLBACK_H