[Newbies] Closure support

Andy Burnett andy.burnett at knowinnovation.com
Fri Oct 30 15:59:16 UTC 2009

Randal said...

<<With classic smalltalk 80 and Squeak:

a := (1 to: 10) do: [:n | [n]].
b := a collect: [:each | each value].
b will have something like #(10 10 10 10 ...).

The problem is that the :n in each block ([n]) is shared as one variable.
In a true closure, which modern Squeak and Pharo provide, we get the proper
#(1 2 3 4 ... 10).  That's because each apperance of "n" is "closed" with
respect to the newly created block.>>

Thanks for explaining the difference between blocks and closures. I think I
new understand that.  And, your example raised a new question for me.

What does the inner 'block' in [:n | [n]] actually do?

Out of curiosity I tried changing it to [:n | [n*10]], expecting the numbers
to be ten times bigger, but they were stil 1, 2, 3...  I also tried removing
the whole block, and b still evaluated to the same values.

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