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digitalmars.D - A suggestion on keyword for_each

reply "SteveGuo" <steveguo outlook.com> writes:
I suggest that change keyword *for_each* to *for* since *for* is 
clear enough and
less letters, like C++11 does.
Aug 08 2013
next sibling parent reply "Tyler Jameson Little" <beatgammit gmail.com> writes:
On Friday, 9 August 2013 at 03:30:16 UTC, SteveGuo wrote:

 I suggest that change keyword *for_each* to *for* since *for* 
 is clear enough and
 less letters, like C++11 does.


Decent suggestion, but I don't think Walter, Andrei or any of the 
committers want to break everyone's code just to shorten some 
syntax.

As a proposal, however, it's not bad, and like you say it exists 
in other languages:

     // Go
     for key, val := range x {} // where x is an array, slice or 
map
     // Java
     for (int x in y) {}
     // C++11
     for (int &x : y) {}
     // Python (or use iter(), range(), xrange(), etc)
     for x in y: pass

Which are similar to D's foreach:

     foreach (key, value; x) {} // where x is a suitable range

I agree that the following would be unambiguous (whichever syntax 
we decide is better):

     for (key, value; x) {}
     for (key, value : x) {}

But it doesn't offer enough benefit to make a breaking change or 
introduce redundant syntax. Saving 4 chararters isn't enough 
justification.

Also, I don't particularly like for_reverse, since you can't use 
a traditional for-loop syntax with for_reverse:

     // would be syntax error
     for_reverse (i = 0; i < 5; i++) {}
     // but this works just fine
     foreach_reverse(i; 0 .. 5);

And D doesn't stand alone in the 'foreach' arena:


     foreach(int x in y) {}
     // Perl
     foreach ( arr) {
         print $_;
     }
     // PHP
     foreach($set as $value) {}
     foreach ($set as $key => $value) {}
     // Scala
     some_items foreach println

I don't really see a compelling reason to switch. Then again, 
this is only my opinion, so I can't speak for the community.
Aug 09 2013
parent reply "Tobias Pankrath" <tobias pankrath.net> writes:
On Friday, 9 August 2013 at 14:51:05 UTC, Tyler Jameson Little 
wrote:

 Also, I don't particularly like for_reverse, since you can't 
 use a traditional for-loop syntax with for_reverse:

     // would be syntax error
     for_reverse (i = 0; i < 5; i++) {}


What do you think would be proper semantics for this?
Aug 09 2013
parent reply "Tyler Jameson Little" <beatgammit gmail.com> writes:
On Friday, 9 August 2013 at 15:20:38 UTC, Tobias Pankrath wrote:

 On Friday, 9 August 2013 at 14:51:05 UTC, Tyler Jameson Little 
 wrote:

 Also, I don't particularly like for_reverse, since you can't 
 use a traditional for-loop syntax with for_reverse:

    // would be syntax error
    for_reverse (i = 0; i < 5; i++) {}


 What do you think would be proper semantics for this?


If the expression is simple enough, it's not out of the question 
for a new programmer to think it will do the same thing as the 
for version, but backwards.

I like foreach and foreach_reverse, because all uses of foreach 
can be foreach_reverse'd (except maybe some ranges), but the same 
does not apply in for. It lacks symmetry, which kind of bothers 
me.

I would prefer a step operator like Python's:

     int[] arr;
     // these two are equivalent
     foreach(x; arr[0 .. $ : -1]) {}
     foreach_reverse(x; arr[0 .. $]) {}

And for ranges:

     auto arr = genRange!int();
     foreach(x; arr.step(-1)) {}

Then I could grab every other one with a step of 2, every third 
with 3, etc. This would not require copying slices or ranges, but 
would be some nice syntax sugar. The index values in the foreach 
would be actual indexes into the slice/range.

If we got this feature, both foreach & foreach_reverse could 
probably be deprecated and merged into for (with no for_reverse). 
This is a pretty substantial change to the language though, so I 
doubt it will make it in.
Aug 09 2013
parent reply "Dicebot" <public dicebot.lv> writes:
`foreach_reverse` is a major design mistake considering the fact 
that it requires a very specific range type, contrary to normal 
range. For lot of ranges concept of iteration order is simply not 
defined making `foreach_reverse` useless. And in rare cases when 
it is needed, it can be replaced with plain `for`.

Hardly does any harm, but definitely not worth putting any 
efforts into it.
Aug 09 2013
parent "monarch_dodra" <monarchdodra gmail.com> writes:
On Saturday, 10 August 2013 at 01:33:58 UTC, Dicebot wrote:

 `foreach_reverse` is a major design mistake considering the 
 fact that it requires a very specific range type, contrary to 
 normal range. For lot of ranges concept of iteration order is 
 simply not defined making `foreach_reverse` useless. And in 
 rare cases when it is needed, it can be replaced with plain 
 `for`.

 Hardly does any harm, but definitely not worth putting any 
 efforts into it.


foreach (foreach_reverse) work like a charm for iterating over 
dchars in a narrow string though.
Aug 10 2013
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/9/13, SteveGuo <steveguo outlook.com> wrote:

 I suggest that change keyword *for_each* to *for* since *for* is
 clear enough and
 less letters, like C++11 does.


Not gonna happen. What's this obsession with less letters? foreach is
common among many modern languages anyway.
Aug 09 2013
prev sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Friday, August 09, 2013 12:43:08 Andrej Mitrovic wrote:

 On 8/9/13, SteveGuo <steveguo outlook.com> wrote:

 I suggest that change keyword *for_each* to *for* since *for* is
 clear enough and
 less letters, like C++11 does.


 
 Not gonna happen. What's this obsession with less letters? foreach is
 common among many modern languages anyway.


Even if it were better to use for rather than foreach, the reality of the 
matter is that at this point in the game, it makes no sense to make changes 
like that. It would break lots of code without actually providing any more 
functionality or fixing any bugs or design flaws in the language.

Now, on top of that, you _couldn't_ use for in place of foreach thanks to how 
crazy versatile D's for loops are (you can put pretty much _anything_ in front 
of the first semicolon - including blocks of code with other for loops). 
Without foreach, there's no way for the compiler to distintguish between when 
you want foreach and when you want a normal for loop. C++ can get away with it 
because its for loops aren't as fancy.

- Jonathan M Davis
Aug 09 2013