and it's faster for not having to generate an extra array:

use warnings;
use strict;
use Benchmark qw(cmpthese);

my @arr = (0,3,4,5,8,10,12,15, 1..999999);

cmpthese (-2,
        {
        mapgrep => sub {map {$arr[$_]} grep {$_ & 1} 1..$#arr},
        slice => sub {@arr[ grep {$_ & 1} 1..$#arr ];},
        grep => sub {my $ind = 0; grep {$ind++ % 2} @arr},
        push => sub {my @var; push(@var, $arr[$_*2+1]) for 0..int(@arr
+/2)-1},
        map => sub {map { $arr[$_*2+1] } 0..int(@arr/2)-1},
        }
    );

[download]

Prints:

# my @arr = (0,3,4,5,8,10,12,15, 1..999999);

          Rate mapgrep   slice    push     map    grep
mapgrep 2.02/s      --    -29%    -35%    -38%    -40%
slice   2.84/s     40%      --     -9%    -13%    -16%
push    3.11/s     54%      9%      --     -5%     -8%
map     3.27/s     62%     15%      5%      --     -3%
grep    3.37/s     66%     18%      8%      3%      --

# my @arr = (0,3,4,5,8,10,12,15);

            Rate    push mapgrep   slice     map    grep
push    160309/s      --    -30%    -39%    -50%    -54%
mapgrep 229948/s     43%      --    -12%    -28%    -34%
slice   261705/s     63%     14%      --    -18%    -25%
map     319334/s     99%     39%     22%      --     -9%
grep    350258/s    118%     52%     34%     10%      --

[download]

The performance holds pretty much regardless of size.

Update: more cases added

DWIM is Perl's answer to Gödel

In reply to Re^2: Quicly extracting odd index elements in the array with grep by GrandFather
in thread Quicly extracting odd index elements in the array with grep by Anonymous Monk

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