A question about returning values from a block

Hi all,

If I write the following code to experiment with squeak's block closures I get the expected answer:
factorial := [:n | (n=1) ifTrue: [1] ifFalse: [n * (factorial value: (n - 1))]].
factorial 3. -> 6

In this case it appears that the block is implicitly returning the last object, ie: return 1 in the ifTrue: case.  If I change the code to explicitly return the 1 ie:
factorial := [:n | (n=1) ifTrue: [^1] ifFalse: [n * (factorial value: (n - 1))]].
factorial 3. -> An error indicating that the block cannot return.

My question is this:  Why is the implicit return of values allowed and not the explicit?  Is there a best practice for dealing with block closures in smalltalk, such that we should only be using implicit returns?

Thanks for your help,
Jeff G.

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An explicit "answer" from a block exits the method in which the
block is defined.  This is often used for "easy answers" in a method:

someMethodFor: aValue

  aValue < 3 ifTrue: [^7].
  aValue > 10 ifTrue: [^aValue * 10].
  ^aValue complexExpressionHere.

As you discovered, if you don't answer from a block, the block's value is the
last expression evaluated.

You actually *can* return a value from the "middle" of a block, but at that
point, the code within the block is better factored out as a separate method.
In fact, nested blocks and complex blocks and desire to have complex control
inside a block are all signs that you aren't yet thinking in terms of small,
single-purpose methods.

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Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
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