Javascript生成器函数 - 用C ++编写 [英] Javascript generator function -- written in C++

问题描述

使用V8 C ++ API，如何实现生成器接口以在Javascript中使用？我想创建一个对象，可以用作 for-of 循环的迭代器。

Using the V8 C++ API, how can I implement the generator interface for use in Javascript? I'd like to create an object that can be used as the iterator for a for-of loop.

推荐答案

看起来第一件事就是检查 Symbol.iterator 的属性查找：

Looks like the first thing that's necessary is to check for a property lookup for Symbol.iterator:

NAN_PROPERTY_GETTER(My_Obj::Getter) {
  auto self = Nan::ObjectWrap::Unwrap<My_Obj>(info.This());
  if (property->IsSymbol()) {
    if (Nan::Equals(property, v8::Symbol::GetIterator(info.GetIsolate())).FromJust()) {
      ...

使用不带参数的函数进行响应。该函数返回一个对象，其 next 属性设置为另一个函数：

Respond with a function that takes no arguments. The function returns an object with a next property set to another function:

      ...
      auto iter_template = Nan::New<v8::FunctionTemplate>();
      Nan::SetCallHandler(iter_template, [](const Nan::FunctionCallbackInfo<v8::Value> &info) {
          auto next_template = Nan::New<v8::FunctionTemplate>();
          Nan::SetCallHandler(next_template, My_Obj::next, info.Data());
          auto obj = Nan::New<v8::Object>();
          Nan::Set(obj, Nan::New<v8::String>("next").ToLocalChecked(),
                   next_template->GetFunction());
          info.GetReturnValue().Set(obj);
        }, info.This());
      info.GetReturnValue().Set(iter_template->GetFunction());
      ...

next 函数也不带参数。它在每次调用时按顺序返回迭代值。我正在使用C ++迭代器：

The next function also takes no arguments. It returns iteration values sequentially on each call. I'm using a C++ iterator for this:

NAN_METHOD(My_Obj::next) {
  auto self = Nan::ObjectWrap::Unwrap<My_Obj>(info.Data().As<v8::Object>());
  bool done = self->iter == self->contents.end();
  auto obj = Nan::New<v8::Object>();
  Nan::Set(obj, Nan::New<v8::String>("done").ToLocalChecked(),
           Nan::New<v8::Boolean>(done));
  if (!done) {
    Nan::Set(obj, Nan::New<v8::String>("value").ToLocalChecked(),
             Nan::New<v8::String>(self->iter->first.c_str()).ToLocalChecked());
  }
  self->iter++;
  info.GetReturnValue().Set(obj);
}

我将状态保存在包装对象本身中。这使得这个生成器不可重入。对于读/写对象来说这可能是好的，因为可能需要另外一种状态保持方法。

I'm keeping state in the wrapped object itself. That makes this generator non-reentrant. That's probably fine for a read/write object, for something read-only another state-keeping approach is probably warranted.

示例对象的完整代码可用。

这篇关于Javascript生成器函数 - 用C ++编写的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！