Dear monks,

When I run the following code:

#!/usr/bin/perl

use strict;
use feature 'say';

sub foo {
    my @a = 'aaaaa' .. 'zzzzz';
    say time;
    return [ @a ];
}

say time;
my $a = foo();
say time;

[download]

I get this for output:

1370302025
1370302028
1370302032

[download]

Whereas, when I run this code:

#!/usr/bin/perl

use strict;
use feature 'say';

sub foo {
    my @a = 'aaaaa' .. 'zzzzz';
    say time;
    return \@a;
}

say time;
my $a = foo();
say time;

[download]

I get this output:

1370302601
1370302604
1370302604

[download]

In other words, in the former case, two huge arrays are created, but in the latter case, only one huge array is created. My question is: Why doesn't perl optimize the former code to only produce one huge array? It must know that the reference count on @a goes to zero at the same time it's copied. Can't it optimize the former's return statement to work just like the latter's? Is it really as simple as it seems, or am I overlooking some complicating factor(s)?

In reply to Why doesn't perl optimize this? by nbtrap

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