Fwd: when iterating over a collection how to determine the current objects index

March 16, 2015

      ---------- Forwarded message ----------
From: Nicolai Hess <nicolaihess@web.de>
Date: 2015-03-16 13:40 GMT+01:00
Subject: Re: [Pharo-users] when iterating over a collection how to
determine the current objects index
To: "jtuchel@objektfabrik.de" <jtuchel@objektfabrik.de>

2015-03-16 12:19 GMT+01:00 jtuchel@objektfabrik.de <jtuchel@objektfabrik.de>
:
...
Nicolai,
Am 16.03.15 um 11:59 schrieb Nicolai Hess:
2015-03-14 11:55 GMT+01:00 Sean P. DeNigris <sean@clipperadams.com>:
...
Marcus Denker-4 wrote
...
which version do we pick? We should pick one, rename the callers
As someone mentioned earlier in the thread, #doWithIndex: has the
advantage
of mirroring the argument order (although this still should be
documented),
and it's the one most people are probably most familiar with, so IMHO it
makes sense to standardize on that.
I like withIndexDo: because code like
so how would you name the current #do: if you had the choice?
I still think this looks very logical:
#do:
#do:separatedBy:
#doWithIndex:
#doWithSomeOtherSpecialty:andEvenMoreStuff:
And then there still ist the question if the order of the arguments should
be changed:
today:
do: [:each| ]
doWithIndex: [:each :index| ]
future:
do: [:each| ]
withIndexDo: [:idx :each | ]
Do you really think that is better?
I think that if we move the withIndex part to the beginning of the
message, it overstates the importance of the fact that we also need the
index inside the iteration block.
aCollection withIndexDo: aBlock
 reads like
 "a collection with index"  do
This would make sense if it was a Collection with an Index.
no, that is the point.
A collection with no index:
aCollection do:

A collection with no index, but iterator over it like it had one:
aCollection withIndex  do:
...
From the method comment:
withIndexDo: elementAndIndexBlock
    "Just like with:do: except that the iteration index supplies the second
argument to the block."
it looks like this method derives from :

SequenceableCollection>>#with: otherCollection do: twoArgBlock
    "Evaluate twoArgBlock with corresponding elements from this collection
and otherCollection."
...
If there was an IndexedCollection class and maybe some message like
asIndexedCollection or withIndex, which turns any collection into an
IndexedCollection. Then the message might be a shortcut for "make thsi an
indexed collection and iterate over it using its index" - comparable to
Dictionary>>#keysAndValuesDo: - but please be aware that a Dictionary has
keys and values by its very own nature. A Collection doesn't have an index
(other than the fact that the elements are stored in some non-guarantueed
order).
This may all sound quite picky, but I think this is plain wrong and you
are about to introduce not only incompatible, but also misleading naming
for methods that exist on all Smalltalk dialects.
I don't want to rename it, it is already there. I just said I like the one
better than the other one.
But it is not really important, I am fine  with either or both. This was
just my explanation why I would choose withIndexDo:
...
Joachim
...
-----
Cheers,
Sean
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Nicolai Hess

jtuchel＠objektfabrik.de

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