use warnings;
use strict;

use Data::Dumper;

sub grep_in_place(&@) {
   my ($cb, $array) = @_;
   my $src = -1;
   my $dst = -1;
   while (++$src < @$array) {
      my $keep;
      $keep = $cb->() for $array->[$src];
      $array->[++$dst] = $array->[$src];
   }
   $#$array = $dst;
}

sub grep_and_remove (&\@) {
   my ($cb, $array_ref) = @_;
   my @found;
   my $i = 0;

   GREP:
   while ($i < @{ $array_ref })
   {
       $cb->()
           and push(@found, splice(@{ $array_ref }, $i, 1))
           and next GREP
             for $array_ref->[$i];
       ++$i;
   }

   return @found;
}

my @arr1 = (1,2,3,4,5,6,7,8);
my @arr2 = grep_in_place   { $_ > 4 } @arr1;

my @arr3 = (1,2,3,4,5,6,7,8);
my @arr4 = grep_and_remove { $_ > 4 } @arr3;

print Dumper(\@arr1, \@arr2, \@arr3, \@arr4);

__END__
$VAR1 = [
          1,
          2,
          3,
          4,
          5,
          6,
          7,
          8
        ];
$VAR2 = [
          '-1'
        ];
$VAR3 = [
          1,
          2,
          3,
          4
        ];
$VAR4 = [
          5,
          6,
          7,
          8
        ];