metaprogramming in smalltalk

Please try to understand the following code:

| a b c |

a := 3.
b := 4.
c := '+'.
^a perform: c asSymbol with: b

Georg Heeg eK, Dortmund und Köthen, HR Dortmund A 12812
Wallstraße 22, 06366 Köthen
Tel. +49-3496-214328, Fax +49-3496-214712


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Gesendet: Sonntag, 29. April 2012 10:25

An: [hidden email]

Betreff: [Esug-list] metaprogramming in smalltalk

Hi! Please could you help me understand smalltalk capabilities in
metaprogramming? Q: could I construct arbitrary message by program? Create
keywords from strings and than build sequence of them to make a message. Mm?
Or may be store keywords in variables and then pass variables withing
messages extracting stored keywords?
Am I dreamer?)


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You probably want to do something like this :

| x y plu perf wi args | 

x := 3.

y := 4. 

plu := '+'.

perf := 'perform:withArguments:'.

args := Array new: 1.

args at: 1 put: y.

x perform: perf asSymbol withArguments: args

You should look the class Message too.
(and all other classes and methods like Behavior, Class, Metaclass, Method and Object)

Jean-François

2012/4/29 Vitaly Kosenko <[hidden email]>

Ok. perform: is working for arithmetic but what about perform: itself?

| x y plu perf wi args | 

x := 3.

y := 4. 

plu := '+'.

perf := 'perform:'.

wi := 'with:'.

args := Array new: 3.

args 

at: 1 put: plu asSymbol;

at: 2 put: wi asSymbol;

at: 3 put: y.

x perform: perf asSymbol withArguments: args.

This code tells me that there is wrong number of arguments in permforn:

How can I fix it?

2012/4/29 vittly <[hidden email]>

Mmm thnx for replie! I'll run this code and experemt with it

2012/4/29 Georg Heeg [via Smalltalk] <[hidden email]>

Please try to understand the following code:

| a b c |

a := 3.
b := 4.
c := '+'.
^a perform: c asSymbol with: b

Georg Heeg eK, Dortmund und Köthen, HR Dortmund A 12812
Wallstraße 22, 06366 Köthen
Tel. <a href="tel:%2B49-3496-214328" value="+493496214328" target="_blank">+49-3496-214328, Fax <a href="tel:%2B49-3496-214712" value="+493496214712" target="_blank">+49-3496-214712


-----Ursprüngliche Nachricht-----

Von: [hidden email]
[mailto:[hidden email]] Im Auftrag von vittly

Gesendet: Sonntag, 29. April 2012 10:25

An: [hidden email]

Betreff: [Esug-list] metaprogramming in smalltalk

Hi! Please could you help me understand smalltalk capabilities in
metaprogramming? Q: could I construct arbitrary message by program? Create
keywords from strings and than build sequence of them to make a message. Mm?
Or may be store keywords in variables and then pass variables withing
messages extracting stored keywords?
Am I dreamer?)


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Hi Vitaly!

try to think it like this: #perform:with: is a reflective operation to send messags to an object.  Thus, if you are trying to send an object a message like:

object perform: someSelector with: someArgument.

- The receiver is object
- the selector of the message is #perform:with:
- the arguments of #perform:with: are someSelector and someArgument.

Then, what you have to do is

object
   perform: #perform:with:
   withArguments: { someSelector . someArgument }

Because #perform: and #with: are not two different messages, they are two keywords of the same selector, in the same message.  Then, you have to treat them together.

Cheers,
Guille

2012/4/29 Vitaly Kosenko <[hidden email]>

Nice! Almost as elegant as Ward's legendary 
Symbol>>value: anObject 
^anObject perform: self 

Mickey!) I don't understand how does it help me.

The method is called #perform:with: and it takes two arguments.  

Yes. But what if I need to emulate "x perform: y with: z" - there is three arguments

How can I do this using perform?

Yes, there is Behavior class that compile everything so non can help this method is good. But what about perform? Message class also require selector and what is selector for keyword messages?

2012/4/29 Jean-François LEFEVRE <[hidden email]>

You probably want to do something like this :

| x y plu perf wi args | 

x := 3.

y := 4. 

plu := '+'.

perf := 'perform:withArguments:'.

args := Array new: 1.

args at: 1 put: y.

x perform: perf asSymbol withArguments: args

You should look the class Message too.
(and all other classes and methods like Behavior, Class, Metaclass, Method and Object)

Jean-François

2012/4/29 Vitaly Kosenko <[hidden email]>

Ok. perform: is working for arithmetic but what about perform: itself?

| x y plu perf wi args | 

x := 3.

y := 4. 

plu := '+'.

perf := 'perform:'.

wi := 'with:'.

args := Array new: 3.

args 

at: 1 put: plu asSymbol;

at: 2 put: wi asSymbol;

at: 3 put: y.

x perform: perf asSymbol withArguments: args.

This code tells me that there is wrong number of arguments in permforn:

How can I fix it?

2012/4/29 vittly <[hidden email]>

Mmm thnx for replie! I'll run this code and experemt with it

2012/4/29 Georg Heeg [via Smalltalk] <[hidden email]>

Please try to understand the following code:

| a b c |

a := 3.
b := 4.
c := '+'.
^a perform: c asSymbol with: b

Georg Heeg eK, Dortmund und Köthen, HR Dortmund A 12812
Wallstraße 22, 06366 Köthen
Tel. <a href="tel:%2B49-3496-214328" value="+493496214328" target="_blank">+49-3496-214328, Fax <a href="tel:%2B49-3496-214712" value="+493496214712" target="_blank">+49-3496-214712


-----Ursprüngliche Nachricht-----

Von: [hidden email]
[mailto:[hidden email]] Im Auftrag von vittly

Gesendet: Sonntag, 29. April 2012 10:25

An: [hidden email]

Betreff: [Esug-list] metaprogramming in smalltalk

Hi! Please could you help me understand smalltalk capabilities in
metaprogramming? Q: could I construct arbitrary message by program? Create
keywords from strings and than build sequence of them to make a message. Mm?
Or may be store keywords in variables and then pass variables withing
messages extracting stored keywords?
Am I dreamer?)


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View this message in context:
http://forum.world.st/metaprogramming-in-smalltalk-tp4595928p4595928.html
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NAML

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