binary selectors ambiguity and space

nicolas cellier ncellier at
Wed May 17 17:10:41 UTC 2006

Le Mercredi 17 Mai 2006 18:36, Duncan Mak a écrit :
> On 5/17/06, Hans-Martin Mosner <hmm at> wrote:
> > The second one is not possible with Smalltalk's semantics. Messages are
> > sent to objects, not to variables. So whatever message you send to
> > variable x, it can't cause x to point to another object (with the
> > exception of #become: but that's a special case). Since numeric objects
> > are immutable, you need to have the assignment x := x+1 either
> > implicitly or explicitly somewhere.
> I was thinking of using become: to implement something like this, yeah.

become: Cannot work on Integer, and beware of side effects, value will change 
also for every object pointing on it...

You can simulate this count++ like with an indirection (a special ValueHolder 
subclass Counter) send the #increment message or whatever to the Counter, and 
then retrieve its value, but i don't know if this is interesting, apart 
sharing a common value between multiple objects

counter := Counter new.
names do: [:each | each startsWith: 'a' ifTrue: [count increment]].
^counter value

> It is true that
>     names select: [:each | each startsWith: 'a'] size
> is more elegant than something like:
>     names do: [:each | each startsWith: 'a' ifTrue: [count := count + 1]

     names count: [:each | each startsWith: 'a']

is even more efficient (does not create a copy of the collection)

>  but what if you want to count multiple conditions in a single iteration?
> Duncan.


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