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Re^2: compare arrays numbers

by crashtest (Curate)
on Feb 16, 2010 at 19:11 UTC ( #823532=note: print w/replies, xml ) Need Help??

in reply to Re: compare arrays numbers
in thread compare arrays numbers

You seem to be editing your post continuously, I hope by the time I submit this the snippet in question won't be outdated... although you seem to be adding to your examples, not modifying (apparently you're working on 1,001 ways to write a loop)

In example #2:

$a[$_] -= $b[$_] for (),0..$#a; # ^-- ... why?
What is up with the stray ()? Just a typo, or are you doing something else here (I thought you might be somehow forcing list context, but 0..$#a is a list anyway).

Without the spare empty list, the expression evaluates equivalently in my perl (5.10.0).

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Re^3: compare arrays numbers
by ikegami (Pope) on Feb 16, 2010 at 19:13 UTC
    $a[$_] -= $b[$_] for 0..$#a;
    is optimised into a counting loop (O(1) memory).
    $a[$_] -= $b[$_] for (),0..$#a;
    is not optimised (O(N) memory).

    but 0..$#a is a list anyway

    ".." is usually the range operator, but not in the first example. In fact, it's not an operator at all there. It's just a separator like the semicolons in for(;;).

    $ perl -MO=Concise,-exec -e'1 for (),$x..$y' 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <;> nextstate(main 1 -e:1) v:{ 4 <0> pushmark sM 5 <|> range(other->6)[t3] lK/1 \ 6 <#> gvsv[*y] s | 7 <1> flop lKM | Range op called goto 8 | to produce a list. f <#> gvsv[*x] s | g <1> flip[t4] lK / 8 <#> gv[*_] s 9 <{> enteriter(next->a last->d redo->a) lK/8 b <0> iter s c <|> and(other->a) vK/1 a <0> unstack v goto b d <2> leaveloop vK/2 e <@> leave[1 ref] vKP/REFC -e syntax OK $ perl -MO=Concise,-exec -e'1 for $x..$y' 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <;> nextstate(main 1 -e:1) v:{ 4 <0> pushmark s 5 <#> gvsv[*x] s \ Args for enteriter/S 6 <#> gvsv[*y] s / 7 <#> gv[*_] s 8 <{> enteriter(next->9 last->c redo->9) lKS/8 a <0> iter s b <|> and(other->9) vK/1 9 <0> unstack v goto a c <2> leaveloop vK/2 d <@> leave[1 ref] vKP/REFC -e syntax OK

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