Smalltalk › Squeak › Squeak - Beginners

Determining the sender in a method

_‹ Previous Topic Next Topic _›

Classic

List

Threaded

3 messages Options

Rob Rothwell

Determining the sender in a method

Is there a way to determine "who" called "me" in a method? Or would doing this just be bad form?

I have a method in an object that creates another object FOR the sender. Rather than pass a parameter, it seemed like it would be nice to just "know" who was asking for the component.

For example, rather than

MyObject>>doSomething
     WidgetBuilderSubclass buildComponentForObject: self anObject.

it would be nice to just

MyObject>>doSomething
     WidgetBuilderSubclass buildComponent

and have

WidgetBuilderSubclass>>buildComponent
     | obj widget |
     obj := self thisMessageSender anObject.
     ...
     ^widget

I am probably asking a question that shows just how much I don't understand "the Smalltalk way!"

Thanks,

Rob

_______________________________________________
Beginners mailing list
[hidden email]
http://lists.squeakfoundation.org/mailman/listinfo/beginners

Randal L. Schwartz

Re: Determining the sender in a method

>>>>> "Rob" == Rob Rothwell <[hidden email]> writes:

Rob> Is there a way to determine "who" called "me" in a method?

Yes, see the methods of "thisContext", a special variable
that represents the currently executing context. The methods
are defined in MethodContext, on which a protocol-browse will reveal
some really interesting (and horribly introspecting) methods, such
as "thisContext sender".

Rob> Or would doing this just be bad form?

Yes. While you *can* do a lot of magic like this, it's probably
best if you avoid it for now. A typical pattern is to pass self:

MyObject>>doSomething
^self otherClass makeSomethingOn: self.

Also note: don't hardwire a helper class name in your methods. Use
a method call to get it, so you'd say:

MyObject>>otherClass
^TheOtherClass

If you hardwire it, it'll make your class much harder to subclass.

--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<[hidden email]> <URL:http://www.stonehenge.com/merlyn/>
Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
See http://methodsandmessages.vox.com/ for Smalltalk and Seaside discussion
_______________________________________________
Beginners mailing list
[hidden email]
http://lists.squeakfoundation.org/mailman/listinfo/beginners

Rob Rothwell

Re: Determining the sender in a method

On Sun, May 25, 2008 at 12:59 AM, Randal L. Schwartz <[hidden email]> wrote:

Rob> Or would doing this just be bad form?

Yes. While you *can* do a lot of magic like this, it's probably
best if you avoid it for now. A typical pattern is to pass self:

MyObject>>doSomething
^self otherClass makeSomethingOn: self.

Thanks...this is almost what I did, lacking the "bad form" MethodContext introspecting methods you described. Although I admit I hardwired it as below, but will rectify that soon enough!

Also note: don't hardwire a helper class name in your methods. Use
a method call to get it, so you'd say:

MyObject>>otherClass
^TheOtherClass

If you hardwire it, it'll make your class much harder to subclass.

Which is what I am doing (subclassing). This "trivial" example shows I am making progress but still somewhat bound by the laws of non-object programming!

Thanks again,

Rob

_______________________________________________
Beginners mailing list
[hidden email]
http://lists.squeakfoundation.org/mailman/listinfo/beginners