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digitalmars.D - Proposal: delegates as aggregates in foreach statements

reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
An idea occurred to me last night, which I'm sure must have come up before.  If
it hasn't, 
I'm shocked, but I'm bringing it up (again?) anyway.  Why not allow a delegate
(or even 
function pointer?) to be used as the "aggregate" parameter to a foreach
statement, 
requiring that it expose the same signature as a valid opApply method?  For
example:





























One could even get real cute and use anonymous delegates:









This, I think, would stand in the place of many uses of iterator objects and
mutators.

-- Chris Nicholson-Sauls
May 05 2006
parent reply Bruno Medeiros <brunodomedeirosATgmail SPAM.com> writes:
Chris Nicholson-Sauls wrote:

 An idea occurred to me last night, which I'm sure must have come up 
 before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
 anyway.  Why not allow a delegate (or even function pointer?) to be used 
 as the "aggregate" parameter to a foreach statement, requiring that it 
 expose the same signature as a valid opApply method?  For example:
 



























 
 One could even get real cute and use anonymous delegates:
 







 
 This, I think, would stand in the place of many uses of iterator objects 
 and mutators.
 
 -- Chris Nicholson-Sauls


Hum, seems like a sound proposal. I think it could be good.


-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D
May 07 2006
parent reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
Bruno Medeiros wrote:

 Chris Nicholson-Sauls wrote:
 

 An idea occurred to me last night, which I'm sure must have come up 
 before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
 anyway.  Why not allow a delegate (or even function pointer?) to be 
 used as the "aggregate" parameter to a foreach statement, requiring 
 that it expose the same signature as a valid opApply method?  For 
 example:





























 One could even get real cute and use anonymous delegates:









 This, I think, would stand in the place of many uses of iterator 
 objects and mutators.

 -- Chris Nicholson-Sauls


 
 
 Hum, seems like a sound proposal. I think it could be good.
 
 


Well at least you thought so.  Doesn't look like it caught anyone else's eye.

-- Chris Nicholson-Sauls
May 14 2006
parent reply James Dunne <james.jdunne gmail.com> writes:
Chris Nicholson-Sauls wrote:

 Bruno Medeiros wrote:
 

 Chris Nicholson-Sauls wrote:


 An idea occurred to me last night, which I'm sure must have come up 
 before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
 anyway.  Why not allow a delegate (or even function pointer?) to be 
 used as the "aggregate" parameter to a foreach statement, requiring 
 that it expose the same signature as a valid opApply method?  For 
 example:





























 One could even get real cute and use anonymous delegates:









 This, I think, would stand in the place of many uses of iterator 
 objects and mutators.

 -- Chris Nicholson-Sauls




 Hum, seems like a sound proposal. I think it could be good.


 
 Well at least you thought so.  Doesn't look like it caught anyone else's 
 eye.
 
 -- Chris Nicholson-Sauls


Just because nobody replies doesn't mean nobody reads.  There's a lot of 
content to plow through during the weekdays on this newsgroup.  I find 
myself guilty of "Mark Thread As Read" (Thunderbird) a lot recently for 
the threads I'm not interested in...

Anyway, about your proposal...

I don't much see much utility in *anonymous* delegates for iteration 
(lots of code duplication for commonly-iterated objects; and what's the 
point of including complex iterator code next to the body of the 
iteration itself?).

But, being able to select an iterator method for a class without 
breaking that method into its own iterator object does have its uses. 
For instance, reverse iteration and tree-walkers (pre-order, in-order, 
post-order, etc.) look to be good candidates here.

-- 
Regards,
James Dunne
May 14 2006
parent reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
James Dunne wrote:

 Chris Nicholson-Sauls wrote:
 

 Bruno Medeiros wrote:


 Chris Nicholson-Sauls wrote:


 An idea occurred to me last night, which I'm sure must have come up 
 before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
 anyway.  Why not allow a delegate (or even function pointer?) to be 
 used as the "aggregate" parameter to a foreach statement, requiring 
 that it expose the same signature as a valid opApply method?  For 
 example:





























 One could even get real cute and use anonymous delegates:









 This, I think, would stand in the place of many uses of iterator 
 objects and mutators.

 -- Chris Nicholson-Sauls





 Hum, seems like a sound proposal. I think it could be good.


 Well at least you thought so.  Doesn't look like it caught anyone 
 else's eye.

 -- Chris Nicholson-Sauls


 
 
 Just because nobody replies doesn't mean nobody reads.  There's a lot of 
 content to plow through during the weekdays on this newsgroup.  I find 
 myself guilty of "Mark Thread As Read" (Thunderbird) a lot recently for 
 the threads I'm not interested in...


True enough.  I didn't really mean anything scathing by it, anyhow.  Honestly,
it was a 
bump message.  :)


 Anyway, about your proposal...
 
 I don't much see much utility in *anonymous* delegates for iteration 
 (lots of code duplication for commonly-iterated objects; and what's the 
 point of including complex iterator code next to the body of the 
 iteration itself?).
 
 But, being able to select an iterator method for a class without 
 breaking that method into its own iterator object does have its uses. 
 For instance, reverse iteration and tree-walkers (pre-order, in-order, 
 post-order, etc.) look to be good candidates here.
 


I think what I had in mind (and just didn't "vocalize") in using anonymous
delegates, was 
to use them like wrappers around a list of other delegate calls or the like
(multi-phase 
looping, perhaps).  I do see your point that in most cases if you were going to
do that, 
you may as well just write the logic into the iteration block itself.  The
tree-walkers 
and suchlike that you mention, though -- that's exactly the sort of thing I'm
after. 
Being able to just do (foreach (i, x; &tree.walkInOrder) {...}) with
.walkInOrder() being 
a simple method would be, pardon the colloquialism, wicked sweet.

-- Chris Nicholson-Sauls
May 15 2006
next sibling parent Oskar Linde <oskar.lindeREM OVEgmail.com> writes:
Chris Nicholson-Sauls skrev:


 I think what I had in mind (and just didn't "vocalize") in using 
 anonymous delegates, was to use them like wrappers around a list of 
 other delegate calls or the like (multi-phase looping, perhaps).  I do 
 see your point that in most cases if you were going to do that, you may 
 as well just write the logic into the iteration block itself.  The 
 tree-walkers and suchlike that you mention, though -- that's exactly the 
 sort of thing I'm after. Being able to just do (foreach (i, x; 
 &tree.walkInOrder) {...}) with .walkInOrder() being a simple method 
 would be, pardon the colloquialism, wicked sweet.


You get it almost as sweet and simple by using a a wrapper struct. See 
for instance Andrew Fedoniouk's tree implementation:

http://www.digitalmars.com/d/archives/digitalmars/D/dtl/378.html

That allows:

foreach(Node n; parent.forward) // all children from first to last
foreach(Node n; parent.backward) // all children from last to first
foreach(Node n; parent.deep) // all descendants - children and their

/Oskar
May 15 2006
prev sibling parent James Dunne <james.jdunne gmail.com> writes:
Chris Nicholson-Sauls wrote:

 James Dunne wrote:
 

 Chris Nicholson-Sauls wrote:


 Bruno Medeiros wrote:


 Chris Nicholson-Sauls wrote:


 An idea occurred to me last night, which I'm sure must have come up 
 before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
 anyway.  Why not allow a delegate (or even function pointer?) to be 
 used as the "aggregate" parameter to a foreach statement, requiring 
 that it expose the same signature as a valid opApply method?  For 
 example:





























 One could even get real cute and use anonymous delegates:









 This, I think, would stand in the place of many uses of iterator 
 objects and mutators.

 -- Chris Nicholson-Sauls






 Hum, seems like a sound proposal. I think it could be good.


 Well at least you thought so.  Doesn't look like it caught anyone 
 else's eye.

 -- Chris Nicholson-Sauls




 Just because nobody replies doesn't mean nobody reads.  There's a lot 
 of content to plow through during the weekdays on this newsgroup.  I 
 find myself guilty of "Mark Thread As Read" (Thunderbird) a lot 
 recently for the threads I'm not interested in...


 
 
 True enough.  I didn't really mean anything scathing by it, anyhow.  
 Honestly, it was a bump message.  :)
 


Seems to have worked then...


 Anyway, about your proposal...

 I don't much see much utility in *anonymous* delegates for iteration 
 (lots of code duplication for commonly-iterated objects; and what's 
 the point of including complex iterator code next to the body of the 
 iteration itself?).

 But, being able to select an iterator method for a class without 
 breaking that method into its own iterator object does have its uses. 
 For instance, reverse iteration and tree-walkers (pre-order, in-order, 
 post-order, etc.) look to be good candidates here.


 
 [snip] Being able to just do (foreach (i, x; 
 &tree.walkInOrder) {...}) with .walkInOrder() being a simple method 
 would be, pardon the colloquialism, wicked sweet.
 
 -- Chris Nicholson-Sauls


And how!

-- 
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GCS/MU/S d-pu s:+ a-->? C++++$ UL+++ P--- L+++ !E W-- N++ o? K? w--- O 
M--  V? PS PE Y+ PGP- t+ 5 X+ !R tv-->!tv b- DI++(+) D++ G e++>e 
h>--->++ r+++ y+++
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James Dunne
May 15 2006