yourself

Hi,

I'm a bit confused about y ourself. I understand that the definition
of yourself is ^self
But when I browse Object and look at yourself: all I find is the
description string..
"Answer self."

What happened to ^self? Where is the actual code implementing this?

Thanks,

bakki
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I have   ^self in my image
but anyway, by default, if there is ^ in a method, it returns self...
so an empty method (message) actually return self...

Cédrick

2006/8/31, Bakki Kudva <[hidden email]>:
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On 31.08.2006, at 17:35, Bakki Kudva wrote:

> Hi,
>
> I'm a bit confused about y ourself. I understand that the definition
> of yourself is ^self
> But when I browse Object and look at yourself: all I find is the
> description string..
> "Answer self."

> What happened to ^self? Where is the actual code implementing this?
>

self is the default return value. So if you return nothing special,  
the compiler
will add a ^self at the end.

A good rule is to make the ^self explicit as soon as it is important,  
thus
for our lecture (#yourself is covered in 04:
http://www.iam.unibe.ch/~scg/Teaching/Smalltalk/Slides/04Idioms.pdf )

we changed the implementation of #yourself to be

yourself
        "Answer self."
        ^self

This is in 3.9

     Marcus
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I forgot **no**

if there is no $^  in a method ....
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On Aug 31, 2006, at 8:35 AM, Bakki Kudva wrote:

> Hi,
>
> I'm a bit confused about y ourself. I understand that the definition
> of yourself is ^self
> But when I browse Object and look at yourself: all I find is the
> description string..
> "Answer self."
>
> What happened to ^self? Where is the actual code implementing this?

By default, all message sends return an object. If no object is
specified by ^, then self is returned.

Eric

>
> Thanks,
>
> bakki
> _______________________________________________
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>

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Cédrick, Marcus,

Thank you so much for clarifying this for me. I downloaded the
lectures and they look great. I am sure I'll learn a lot from them. If
it is not asking for too much it would  be aweswome if there were mp3
audio files of the lectures to go with the slides. I downloaded the
Abelson Sussman lectures...
http://www.swiss.ai.mit.edu/classes/6.001/abelson-sussman-lectures/
which are fantastic as well...but for Scheme mostly.

Thanks again,

bakki

On 8/31/06, Marcus Denker <[hidden email]> wrote: _______________________________________________
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Hi Bakki,

yourself is used quite often for chaining messages.  Long chains are
definitely bad form but in some cases you are stuck without having yourself.

Take for example

        aCollection add: 'hello'

When you first encounter this message many people make the mistake of
believing that add: returns a collection.  You will see bugs created in this
way.  For example someone might write

        "THIS CODE DOES NOT WORK"
        aCollection := aCollection add: 'hello'.

Since after running this code what you get is aCollection = 'hello'.
(Forget that the assignment isn't even necessary for the moment since
aCollection is changed with add, you will still see this).

The result is not what you would expect.

        To fix this you do:

        "THIS CODE DOES WORK"
        aCollection := aCollection add: 'hello'; yourself.

This basically returns the "self" of the previous message instead of the
value that is returned from the previous message.

Also consider this

        MyClass class > createFrom: anOtherObject
                "return to the sender an instance of the receiver setting
anOtherObject to someOtherObject"
                ^(MyClass new)
                        someOtherObject: anOtherObject

if the mutator returns self you are ok if not this will not work.  It
usually does, but other methods may not for example:

        MyClass class > createFrom: anOtherObject
                "return to the sender a processed instance of the receiver
setting anOtherObject to someOtherObject"
                ^(MyClass new)
                        someOtherObject: anOtherObject;
                        processResult

if processResult sets a value on the object and returns the result then you
are stuck.  Fix it with yourself.

        MyClass class > createFrom: anOtherObject
                "return to the sender a processed instance of the receiver
setting anOtherObject to someOtherObject"
                ^(MyClass new)
                        someOtherObject: anOtherObject;
                        processResult;
                        yourself.


Hope that helps!

Happy Coding

Ron Teitelbaum
President / Principal Software Engineer
US Medical Record Specialists
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On 31.08.2006, at 18:01, Bakki Kudva wrote:

> Cédrick, Marcus,
>
> Thank you so much for clarifying this for me. I downloaded the
> lectures and they look great. I am sure I'll learn a lot from them.

A link with all the slides (and exercises) is available here:

http://www.iam.unibe.ch/~scg/Teaching/Smalltalk/index.html

> If
> it is not asking for too much it would  be aweswome if there were mp3
> audio files of the lectures to go with the slides. I downloaded the
> Abelson Sussman lectures...
> http://www.swiss.ai.mit.edu/classes/6.001/abelson-sussman-lectures/
> which are fantastic as well...but for Scheme mostly.
>

I know... videos are a very nice thing. But we don't have any of the
SCG Smalltalk lecture...

There are some Smalltalk/Squeak related videos on Google:

http://video.google.com/videosearch?q=label:esug

e.g. Dan Ingall's classic video about OO, some talks about Seaside,
lots of cool Alan Kay talks (I love the OOPSLA97 keynote...).

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Hi Ron,

I was reading the section on yourself in Kent Beck's Best Practices
Patterns book. Your examples made it even more clearer how to use
cascading with yourself Thanks a lot.

bakki

On 8/31/06, Ron Teitelbaum <[hidden email]> wrote:
> Hi Bakki,
>
> yourself is used quite often for chaining messages.  Long chains are
> definitely bad form but in some cases you are stuck without having yourself.
<snip>
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