Implementing Event Handling, Part Two

re: Implementing Event Handling, Part Two

ptrex — Tue, 29 Jul 2008 03:13:37 GMT

I was planning on implementing a script-host in my application, and let user scripts to respons to event raised by the application. Most of the code is not COM-code, so I though that I could use code-generation (from XML, for instance) to create files as follows:

// CClass.h

class CClass {

public:

IDispatch getIDispatch();

ITypeInfo getITypeInfo();

// members from XML

};

//CClass.cpp

IDispatch CClass::getIDispatch(

// CreateDispTypeInfo

// CreateStdDispatch ...

);

ITypeInfo CClass::getITypeInfo() {

// CreateDispTypeInfo

}

void CClass::memberFromXML() {

// call CClassImpl::memberFromClass - this would be the class that the user will actually write

}

// rest of members from XML

But reading this post makes me wonder - what do I need to do so that the scripts could implement event handlers? I hoped for something like:

// C++

myScriptEngine.AddNamedItem("FileMon", SCRIPTITEM_ISSOURCE)

...

// User-attached script

Sub FileMon_OnFileCreate(filename)

MyLog.WriteLine("OMG~~~ somebody crated a file by the amaz1ng name of: " & filename)

End Sub

How feasible is this and what do I need to do with my C++ classes/interfaces to support this? Note that the rest of the code doesn't use COM in any way, and this is probably the only place in which it is going to be used, so I'd prefer as few changes as possible (if it can be achieved through code-generation however, it's not as bad). Also, registration is highly discouraged. After all, it's practically an internal class.

re: Implementing Event Handling, Part Two

Eric Lippert — Thu, 22 Sep 2005 19:56:25 GMT

That preview compiler is a decent demo and research tool, but it is not a production-quality compiler. We're going to have to do a huge amount of refactoring work in the real compiler to get C# 3.0 features generating more optimal code and working with IDE features such as Intellisense.

So there are huge implications for the refactoring and redesign of the current C# 2.0 codebase. There's plenty of work to keep us going for quite a while here. The demo compiler is just the first step in a long process.

re: Implementing Event Handling, Part Two

RIchB — Thu, 22 Sep 2005 19:05:07 GMT

> trying to understand the implications that LINQ
> features are going to have on the current
> implementation

Surely you already know the implications? The preview compiler contains LINQ support already! The only (announced) planned LINQ stuff that wasn't in the preview were lambda statements - which are probably not capable of being compiled to expression trees and are therefore virtually identical to anonymous methods from C# v2.