gin/function_template.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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#ifndef GIN_FUNCTION_TEMPLATE_H_
#define GIN_FUNCTION_TEMPLATE_H_

$var MAX_ARITY = 4

// Copyright 2013 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.

#include "base/callback.h"
#include "base/logging.h"
#include "gin/arguments.h"
#include "gin/converter.h"
#include "gin/gin_export.h"
#include "gin/handle.h"
#include "gin/public/gin_embedders.h"
#include "gin/public/wrapper_info.h"
#include "gin/wrappable.h"

#include "v8/include/v8.h"

namespace gin {

class PerIsolateData;

enum CreateFunctionTemplateFlags {
  HolderIsFirstArgument = 1 << 0,
};

namespace internal {

template<typename T>
struct CallbackParamTraits {
  typedef T LocalType;
};
template<typename T>
struct CallbackParamTraits<const T&> {
  typedef T LocalType;
};
template<typename T>
struct CallbackParamTraits<const T*> {
  typedef T* LocalType;
};


// CallbackHolder and CallbackHolderBase are used to pass a base::Callback from
// CreateFunctionTemplate through v8 (via v8::FunctionTemplate) to 
// DispatchToCallback, where it is invoked.
//
// v8::FunctionTemplate only supports passing void* as data so how do we know
// when to delete the base::Callback? That's where CallbackHolderBase comes in.
// It inherits from Wrappable, which delete itself when both (a) the refcount
// via base::RefCounted has dropped to zero, and (b) there are no more
// JavaScript references in V8.

// This simple base class is used so that we can share a single object template
// among every CallbackHolder instance.
class GIN_EXPORT CallbackHolderBase : public Wrappable<CallbackHolderBase> {
 public:
  static WrapperInfo kWrapperInfo;

 protected:
  virtual ~CallbackHolderBase() {}
};

template<typename Sig>
class CallbackHolder : public CallbackHolderBase {
 public:
  CallbackHolder(const base::Callback<Sig>& callback, int flags)
      : callback(callback), flags(flags) {}
  base::Callback<Sig> callback;
  int flags;
 private:
  virtual ~CallbackHolder() {}
};


// This set of templates invokes a base::Callback, converts the return type to a
// JavaScript value, and returns that value to script via the provided
// gin::Arguments object.
//
// In C++, you can declare the function foo(void), but you can't pass a void
// expression to foo. As a result, we must specialize the case of Callbacks that
// have the void return type.

$range ARITY 0..MAX_ARITY
$for ARITY [[
$var INV_ARITY = MAX_ARITY - ARITY
$range ARG 1..INV_ARITY
$range VOID INV_ARITY+1..MAX_ARITY

$if ARITY == 0 [[
template<typename R$for ARG [[, typename P$(ARG) = void]]>
struct Invoker {
]] $else [[
template<typename R$for ARG [[, typename P$(ARG)]]>
struct Invoker<R$for ARG [[, P$(ARG)]]$for VOID [[, void]]> {
]]

  inline static void Go(
      Arguments* args,
      const base::Callback<R($for ARG , [[P$(ARG)]])>& callback$for ARG [[, 
      const P$(ARG)& a$(ARG)]]) {
    args->Return(callback.Run($for ARG, [[a$(ARG)]]));
  }
};
template<$for ARG , [[typename P$(ARG)]]>
struct Invoker<void$for ARG [[, P$(ARG)]]$for VOID [[, void]]> {
  inline static void Go(
      Arguments* args,
      const base::Callback<void($for ARG , [[P$(ARG)]])>& callback$for ARG [[,
      const P$(ARG)& a$(ARG)]]) {
    callback.Run($for ARG, [[a$(ARG)]]);
  }
};


]]

template<typename T>
bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
                     T* result) {
  if (is_first && (create_flags & HolderIsFirstArgument) != 0) {
    return args->GetHolder(result);
  } else {
    return args->GetNext(result);
  }
}

// For advanced use cases, we allow callers to request the unparsed Arguments
// object and poke around in it directly.
inline bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
                            Arguments* result) {
  *result = *args;
  return true;
}


// DispatchToCallback converts all the JavaScript arguments to C++ types and
// invokes the base::Callback.
template<typename Sig>
struct Dispatcher {
};

$range ARITY 0..MAX_ARITY
$for ARITY [[
$range ARG 1..ARITY

template<typename R$for ARG [[, typename P$(ARG)]]>
struct Dispatcher<R($for ARG , [[P$(ARG)]])> {
  static void DispatchToCallback(
      const v8::FunctionCallbackInfo<v8::Value>& info) {
    Arguments args(info);
    CallbackHolderBase* holder_base = NULL;
    CHECK(args.GetData(&holder_base));

    typedef CallbackHolder<R($for ARG , [[P$(ARG)]])> HolderT;
    HolderT* holder = static_cast<HolderT*>(holder_base);

$if ARITY != 0 [[


$for ARG [[    typename CallbackParamTraits<P$(ARG)>::LocalType a$(ARG);

]]
    if ($for ARG  ||
        [[!GetNextArgument(&args, holder->flags, $if ARG == 1 [[true]] $else [[false]], &a$(ARG))]]) {
      args.ThrowError();
      return;
    }

]]

    Invoker<R$for ARG [[, P$(ARG)]]>::Go(&args, holder->callback$for ARG [[, a$(ARG)]]);
  }
};

]]

}  // namespace internal


// This should be called once per-isolate to initialize the function template
// system.
GIN_EXPORT void InitFunctionTemplates(PerIsolateData* isolate_data);


// CreateFunctionTemplate creates a v8::FunctionTemplate that will create
// JavaScript functions that execute a provided C++ function or base::Callback.
// JavaScript arguments are automatically converted via gin::Converter, as is
// the return value of the C++ function, if any.
template<typename Sig>
v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
    v8::Isolate* isolate, const base::Callback<Sig> callback,
    int callback_flags = 0) {
  typedef internal::CallbackHolder<Sig> HolderT;
  gin::Handle<HolderT> holder = CreateHandle(
      isolate, new HolderT(callback, callback_flags));
  return v8::FunctionTemplate::New(
      &internal::Dispatcher<Sig>::DispatchToCallback,
      ConvertToV8<internal::CallbackHolderBase*>(isolate, holder.get()));
}

}  // namespace gin

#endif  // GIN_FUNCTION_TEMPLATE_H_