Cobra Forums

Csaba wrote:Hi Chuck

Cobra is a wonderful language and I really hope it will succeed. Among many advantages with Cobra, I really like that Cobra is written in Cobra. Due to this, I think Cobra will develop and improve fast, if there is enough funding, my main concern.

Csaba wrote:I hope that methods will be first class objects in Cobra so that the Delegate/Event mess in C# and VB will be absent from Cobra. I’m not even able to count all the reserved words that are involved in the Delegate/Event mess. Not to mention all the confusing writing about delegates and events. Another wish, I haven’t seen if there is support for try-catch in Cobra, but I assume it will be implemented?

class X
    event onSomething(sender as X, args as EventArgs)

    def foo
        # ...
        raise onChange(this, EventArgs())

class Y
    def init
        # ...
        listen x.onChange, ref .handleChange

    def handleChange(x as X, args as EventArgs)
        # ...

# or

class Z
    var _x = X()
    def handleChange(x as X, args as EventArgs)
        handles _x.onChange
        # ...

Csaba wrote:I certainly would switch to Cobra from VB if it were possible in practices; Cobra cleans up everything I think is bad with VB. But for that Cobra needs: Support for Cobra in Visual Studio (or SharpDevelop?) for three reasons:

Csaba wrote:Further to broaden the acceptance for Cobra, someone should have to port Cobra to the JVM. I might not be a giant issue since Cobra is written in Cobra and Scala, Jython and JRuby exist on the JVM. But nonetheless the porting will require lot of clever work, and thus some funding.

Csaba wrote:I really would love if Cobra could replace VB and C# and even Java. But remember, C++ killed Ada and Java killed Modula-3, the world is not fair!

Csaba wrote:God Luck!
Csaba

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aSub =anotherSub

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Public Delegate Sub AnyParameterLessSub()

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Dim aSubDelegate As AnyParameterLessSub = New AnyParameterLessSub             (AddressOf anotherSub)

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Event, WithEvent, Handles, AddHandler, RemoveHandler, AddressOf, RaiseEvent

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Public Event BehaviourEvent()

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Dim WithEvents aButton As New System.Windows.Forms.Button

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Sub SomeBehaviour Handles aButton.Click

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RaiseEvent Click

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anObject.Behaviour = modifiedBehaviour

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anObject.Behaviour

Csaba wrote:Hi Chuck

The delegate and event concepts are important and have to be implemented in Cobra. I will try to describe what I mean with the delegate an event mess in VB. This description is a black box perspective on delegates and events. I have never looked at any dissembled code and will probably never do it. Neither am I an expert on these issues, just confused, so I have probably misunderstood many of the issues here In VB you can’t assign directly a method to a variable like this:

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aSub =anotherSub

You have to first declare a delegate:

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Public Delegate Sub AnyParameterLessSub()

Csaba wrote:Then:

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Dim aSubDelegate As AnyParameterLessSub = New AnyParameterLessSub             (AddressOf anotherSub)

An ignorat question, why is AddressOf needed here? It seems that Cobra is using the Ref keyword in similar situations. Is it a problem here to understand that it should be the reference? The delegate class methods like Remove, RemoveAll and Combine do not require the AddressOf a delegate. In VB2005, it is also little tedious to do all the type casting when Remove, RemoveAll and Combine are used. Hopefully, Cobra can simply that.

Csaba wrote:Then comes the event concept with reserved words:

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Event, WithEvent, Handles, AddHandler, RemoveHandler, AddressOf, RaiseEvent

...
I don’t know why it should be possible to inhibit this by declaring an object without the WithEvent keyword. So I think the WithEvent keyword is not necessary.

Csaba wrote:The AddHandler, RemoveHandler used with the AddressOf keyword seems syntactic sugar for the delegate methods. I believe that normal collection methods are easier understood and used (but not the present ,NET delegate methods).

Csaba wrote:The keyword RaiseEvent that executes the methods in the method list connected to the Click event in VB:

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RaiseEvent Click

And RaiseEvent can only be used IN THE SAME method or class that has the event declaration! Why? Delegates don’t have this restriction, and why isn’t the delegate invoke method used instead? This limitation has also given the convention in some places that the method added to the event list should be named On<EventName>.
From a black box perspective, the Event class seems to be a wrapper around the Delegate class. The main advantage with the event concept seems to be that it extends the delegate concept with Handles, so that methods are added automatically to the delegate list by the compiler at compile time. But the restriction with RaiseEvent limits the events usability compared with delegates.

Csaba wrote:I would like that functions in Cobra by default have some delegate functionality so it would be possible to write straight forwardly:

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anObject.Behaviour = modifiedBehaviour

It should used anywhere just like present VB delegates:

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anObject.Behaviour

Csaba wrote:For this, the Cobra delegate should have a subset of the present .NET delegate functionality since each Cobra delegate should have just one method connected to it, not a list of methods. Hopefully, Raise in the Cobra event concept doesn’t have the VB RaiseEvent limitations.

Csaba wrote:Hopefully, this clarifies what I dislike about delegates and events in VB.
Regards
Csaba