Returning a wrapped class from another class

[zbjornson]

I have two C++ classes. A method on one of them is supposed to return a new instance of b. I tried to follow the pattern described here:

// foo.cc
const int argc = 3;
Local<Value> argv[argc] = { NanNew(*arr), NanNew(sw), NanNew(sh) };
Local<Function> cons = Local<Function>::New(Isolate::GetCurrent(), Bar::constructor);
NanReturnValue(cons->NewInstance(argc, argv));

but then:

No instance of overloaded function "v8::Local<T>::New [with T=v8::Function]" matches the argument list. Argument types are: (v8:Isolate *(), v8::Persistent<v8::FunctionTemplate, v8::NonCopyablePersistentTraits<V8::Functiontemplate>>)

I can't find an example of this pattern in the io.js source, and the closest google result is an unanswered SO question. I found one example where a factory method was added to Bar but that seems like it should be unnecessary. Any tips on the pattern to use here? Thanks.

[bnoordhuis]

Bar::constructor is a Persistent<Function>? You need to turn it into a Local first: Local<Function> constructor = Local<Function>::New(isolate, Bar::constructor);.

[zbjornson]

I think that's what I did in the 3rd line of my example unless I'm misreading.

But, Bar::constructor is actually a Persistent<FunctionTemplate>, not a Function. That's what the package I'm updating (node-canvas) had originally and, from my understanding, is the correct type to use for a class returned to JS.

class ImageData: public node::ObjectWrap {
    public:
    static Persistent<FunctionTemplate> constructor;
    static void Initialize(Handle<Object> target);
    //...
    ImageData(uint8_t *data, int width, int height) : _width(width), _height(height), _data(data) {}
    private:
    //...
};

Full context:

• Where I need to return the instance of the other class
• The "other" (Bar or ImageData) class source and header. For now I added a NewInstance method to Bar/ImageData.

Thanks.

[zbjornson]

Erm, think I had the solution in my temporary ImageData factory method, which was to call GetFunction on the ImageData constructor FunctionTemplate:

const int argc = 3;
Local<Value> argv[argc] = { clampedArray, NanNew(sw), NanNew(sh) };
Local<FunctionTemplate> cons = NanNew(ImageData::constructor);
Local<Object> instance = cons->GetFunction()->NewInstance(argc, argv);
NanReturnValue(instance);