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POCalling a function that uses a wrapped object as an argument in Node.js and v8
 

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    <p>I would like to do something like the following in node.js...</p> <p>var a = new A(); var b = new B();</p> <p>//onTick should be a function that takes an instance of B as an argument</p> <p>a.onTick = function(bInst){ .... }</p> <p>a.loop();</p> <p>meaning that A has a property "onTick" which is a function that gets called inside the loop. Note that A and B are defined as C++ wrapped functions, here are the definitions</p> <pre><code>void AClass::Init(Handle&lt;Object&gt; target) { Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(New); tpl-&gt;SetClassName(String::NewSymbol("A")); tpl-&gt;InstanceTemplate()-&gt;SetInternalFieldCount(1); tpl-&gt;PrototypeTemplate()-&gt;Set(String::NewSymbol("tick"), FunctionTemplate::New(Tick)-&gt;GetFunction()); tpl-&gt;PrototypeTemplate()-&gt;Set(String::NewSymbol("loop"), FunctionTemplate::New(Loop)-&gt;GetFunction()); constructor = Persistent&lt;Function&gt;::New(tpl-&gt;GetFunction()); constructor-&gt;InstanceTemplate()-&gt;SetAccessor(String::New("onTick"), GetOnTick, SetOnTick); target-&gt;Set(String::NewSymbol("A"), constructor); } Handle&lt;Value&gt; AClass::New(const v8::Arguments &amp;args) { HandleScope scope; AClass* acls = new AClass(); WrappedAClass* wrappedA = new WrappedAClass(); acls-&gt;wrappedAInst_ = wrappedA; window-&gt;Wrap(args.This()); return args.This(); } Handle&lt;Value&gt; AClass::Loop(const Arguments &amp;args) { HandleScope scope; AClass* acls = ObjectWrap::Unwrap&lt;AClass&gt;(args.This()); acls-&gt;wrappedInst_-&gt;loop(); return scope.Close(Undefined()); } </code></pre> <p>I believe this is how you set the getter and setter of a property</p> <pre><code>Handle&lt;Function&gt; GetOnTick(Local&lt;String&gt; property, const AccessorInfo&amp; info) { AClass* acls = ObjectWrap::Unwrap&lt;AClass&gt;(info.Holder()); return acls-&gt;onTick_; } void SetOnTick(Local&lt;String&gt; property, Local&lt;Function&gt; value, const AccessorInfo&amp; info) { AClass* acls = ObjectWrap::Unwrap&lt;AClass&gt;(info.Holder()); acls-&gt;onTick_ = Persistent&lt;Function&gt;::New(value); //Here's where I know I'm doing it wrong void func(WrappedClassB* wcb) { const unsigned argc = 1; Local&lt;Value&gt; argv[argc] = { Local&lt;Value&gt;::New(BClass::Instantiate(wcb)) }; acls-&gt;onTick_-&gt;Call(Context::GetCurrent()-&gt;Global(), argc, argv); } acls-&gt;wrappedAInst_-&gt;setTickFunc(func); } </code></pre> <p>What I am trying to do is take the function from setting onTick (which takes an instance of Class B) and wrap it inside a function that instatiates a new BClass.</p> <p>Anyways heres the definition for BClass</p> <pre><code>Persistent&lt;Function&gt; BClass::constructor; BClass::BClass() { } BClass::~BClass() { } void BClass::Init(Handle&lt;Object&gt; target) { Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(New); tpl-&gt;SetClassName(String::NewSymbol("B")); tpl-&gt;InstanceTemplate()-&gt;SetInternalFieldCount(1); constructor = Persistent&lt;Function&gt;::New(tpl-&gt;GetFunction()); target-&gt;Set(String::NewSymbol("B"), constructor); } Handle&lt;Value&gt; BClass::New(const v8::Arguments &amp;args) { HandleScope scope; BClass* bcls = new BClass(); bcls-&gt;Wrap(args.This()); WrappedBClass* wrappedB = new WrappedBClass(); bcls-&gt;wrappedBInst_ = wrappedB; return args.This(); } Handle&lt;Value&gt; BClass::Instantiate(const WrappedBClass &amp;wbc) { HandleScope scope; //I know the following is wrong but it shows what I am trying to do BClass* bcls = new BClass(); bcls-&gt;wrappedBInst_ = wbc; return scope.Close(Local&lt;v8::Value&gt;::New(bcls)); } </code></pre> <p>Both AClass and BClass use another C++ class and save the instance as a property (wrappedBInst, wrappedAInst) I believe I need the Instantiate function for when I need to convert an instance of the WrappedBClass into a BClass.</p> <p>WrappedBClass doesn't do anything special but WrappedAClass inherits a class which has a loop and an onTick function, and the onTick function is where I need to call my Javascript function, so in WrappedAClass I overrode onTick and added a setTickFunc function.</p> <pre><code>class WrappedAClass : public InheritedClass{ public: void setTickFunc(void (*func)(WrappedBClass*)){ tickFunc = func; } protected: void tickFunc; virtual void onTick(WrappedBClass* wbc){ if(tickFunc){ tickFunc(wbc); } } } </code></pre> <p>So the only way I think that I can get into the loop and use a javascript function as the onTick function is to first wrap the javascript function into a c++ function and then set that function by calling setTickFunc(). Am I going about this the right way?</p> <p>I'm a decent programmer but just recently started working with C++ so excuse my obvious mistakes, the biggest one is most likely this:</p> <pre><code>void SetOnTick(Local&lt;String&gt; property, Local&lt;Function&gt; value, const AccessorInfo&amp; info) { AClass* acls = ObjectWrap::Unwrap&lt;AClass&gt;(info.Holder()); acls-&gt;onTick_ = Persistent&lt;Function&gt;::New(value); //Here's where I know I'm doing it wrong void func(WrappedClassB* wcb) { const unsigned argc = 1; Local&lt;Value&gt; argv[argc] = { Local&lt;Value&gt;::New(BClass::Instantiate(wcb)) }; acls-&gt;onTick_-&gt;Call(Context::GetCurrent()-&gt;Global(), argc, argv); } acls-&gt;wrappedAInst_-&gt;setTickFunc(func); } </code></pre> <p>I'm still trying to figure out how to create an anonymous function that holds on to the value of a variable from the outside (acls). I don't think closures are valid here, the key is that this function only have one argument (WrappedClassB* wcb) because it needs to be set as the OnTick function.</p>
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