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Category:Smalltalk: Difference between revisions
→A Word About Code Snippets in Rosetta
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(knowing that the "ifXX"-methods send <tt>"value"</tt> to the corresponding arg and return that)
In this style, all of Smalltalk's control structures, loops, enumeration, stream readers and event-
The following is only a tiny subset - there are virtually hundreds or thousands of uses of blocks for control structures in the system.
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[ loop code . condition expression ] whileTrue.
[ loop code ] doWhile:[ condition ].
[ loop code ] doUntil:[ condition ].
n timesRepeat:[ block to be looped over ] "n being an integer"
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=== Return from a Block ===
it should be noted that a " ˆ " (return) inside a block will return from the enclosing method, NOT only from the block. And that this is an essential semantic property of the return (technically, it may be a long return from a deeply nested call hierarchy, possibly involving unwind actions).
This makes it possible to pass a block to eg. collections to enumerate elements up-to and until some condition is met. For example, if we need a helper method, which searches the first element in a dataset to some condition and evaluate an action on it, we can write:
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<lang smalltalk>[ try block to be evaluated ] on:exception do:[:ex | handler code ]</lang>
where '<I>exception</I>' is an Exception class or Signal instance and the '<I>ex</I>' argument provides detail information (where and why) to the hander and also allows control of how to continue afterwards (proceed, return, restart, reject).
<br>The handler basically has the following options:
* ex return - return out of the try block
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Some implementations support source-to-source compilation to C, JavaScript or Java. These may or may not show some limitations in the support for dynamic changes at execution time. Typically, the full dynamic bytecode is used for development, followed by a compilation phase for deployment/packaging.
All Smalltalks use and depend on garbage collection for automatic reclamation of unused objects, and most implementations use modern algorithms such as generation scavenging, incremental background
As message send performance is critical in Smalltalk, highly tuned cache mechanisms have been invented and are used: inline caches, polymorph inline caches, dynamic recompilation based on receiver and/or argument types etc.
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ifTrue:[1]
ifFalse:[ self * (self-1) factorial ]</lang>
(here '<I>self</I>' is the Integer receiver object, and " ˆ " returns a value from the message send).
To get the factorial value, we'd evaluate in a workspace:<lang>10 factorial</lang>
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a) is somewhat inconvenient if the code example consists of multiple methods, possibly in multiple classes.
<br>b) comes with the additional trouble that fileIn formats are different (chunk file, vs. XML file, vs. Monticello, vs. GNU-ST etc.).
For example, for export/import, GNU-ST uses a ''private format'',
<lang smalltalk>Number extend [
my_factorial [
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