(jeffa) 5Re: grep, map vs. foreach performance

It's really quite simple - for and foreach are the same. When you don't care about the value of the current index, don't use it:

@array = ('a'..'z');
print $_,$/ for @array;
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When you do care about the value of the current index, do use it:

printf "%02d: %s\n", $_+1, $array[$_] for 0..$#array;
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When in doubt, check with Deparse.pm:

$ perl -MO=Deparse foo.pl
@array = ('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 
'w', 'x', 'y', 'z');
foreach $_ (@array) {
    print $_, $/;
}
foreach $_ (0 .. $#array) {
    printf "%02d: %s\n", $_ + 1, $array[$_];
}
foo.pl syntax OK
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Comment on (jeffa) 5Re: grep, map vs. foreach performance Select or Download Code

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Re^6: grep, map vs. foreach performance by Flexx (Pilgrim) on Sep 04, 2002 at 16:46 UTC
Hmm.. You missed my point (or you're repeating what I said). I wasn't comparing `for(ARRAY)` with `for(TEMP_ARRAY)`, but `for(ARRAY)` with `for(EXPR;EXPR;EXPR)`. I do know that for and foreach are synonymous words. I was trying to clarify that in `for (@array) {$_++}` `$_` is an implicit alias for the current `@array` element. While in `for (0 .. $#array) {$array[$_]++}` `$_` an alias for the current index. And that, in terms of what to use for what (as you already clarified) was the difference I meant...	[reply] [d/l] [select]
Re^7: grep, map vs. foreach performance by sauoq (Abbot) on Sep 04, 2002 at 21:40 UTC
I do know that for and foreach are synonymous words. I was trying to clarify that in `for (@array) {$_++}` [download] $_ is an implicit alias for the current @array element. While in `for (0 .. $#array) {$array[$_]++}` [download] $_ an alias for the current index. In your second example there, perl has no idea that $_ is an alias for the "current index." All it knows is that it is an alias for the current list element. The difference between the two examples is only in the contents of the list that the for statement is iterating over. -sauoq "My two cents aren't worth a dime.";	[reply] [d/l] [select]
Re^8: grep, map vs. foreach performance by Flexx (Pilgrim) on Sep 05, 2002 at 07:28 UTC
Of course has no idea about what (semanticly) it's an alias for. I just had to find a word (or two) for that anonymous array element (since the range operator creates a temporary array, not a list) it represents, which was an index in our case. I thought that was obvious by not naming it `$current_index`. ;) It's funny that you even brought this up. Seems like Perl has so much magic that one has to point out: "Well, no, Perl does not really understand what you're doing"... That aside, I always thought `$_` knows far too much! ;) So long, Flexx	[reply] [d/l] [select]