Yes but ref aliasing doesn't allow slicing a subset out of it.

Yes, this is true. But earlier you said you would abstract it out into a function anyway, so it doesn't really matter how it's implemented ;-)

<update> See also </update>

use warnings;
use strict;

sub arr_alias_1 {
    my ($arr,@i) = @_;
    return sub {\@_}->(@$arr[@i]);
}

use Data::Alias 'alias';
sub arr_alias_2 {
    my ($arr,@i) = @_;
    alias my @x = @$arr[@i];
    return \@x;
}

sub arr_alias_3 {
    my ($arr,@i) = @_;
    use 5.022;  # for refaliasing
    use experimental 'refaliasing';
    my @x;
    #(\@x) = \(@$arr[@i]);  # Assigned value is not an ARRAY reference
    #\@x[0..$#i] = \(@$arr[@i]);  # @x is just undefs?
    \$x[@x] = \$$arr[$_] for @i;  # works
    return \@x;
}

sub hash_alias_1 {
    my ($hash,@k) = @_;
    ... # not possible in pure Perl?
}

use Data::Alias 'alias';
sub hash_alias_2 {
    my ($hash,@k) = @_;
    use 5.020; # for Key/Value Hash Slices
    alias my %x = %$hash{@k};
    return \%x;
}

sub hash_alias_3 {
    my ($hash,@k) = @_;
    use 5.022;  # for refaliasing
    use experimental 'refaliasing';
    my %x;
    #\(@x{@k}) = \(@$hash{@k});    # values of %x are undefs?
    \$x{$_} = \$$hash{$_} for @k;  # works
    return \%x;
}

# arr_alias_4 and hash_alias_4 could be implemented with "tie"...

use Test::More tests=>10;

for my $aa (\&arr_alias_1,\&arr_alias_2,\&arr_alias_3) {
    my @arr = ('a'..'z');
    my $subset = $aa->(\@arr, 5..10);
    is_deeply $subset, ['f'..'k'] or diag explain $subset;
    $subset->[3] = 9;
    is_deeply \@arr, ['a'..'h',9,'j'..'z'];
}

for my $ha (\&hash_alias_2,\&hash_alias_3) {
    my %hash = map {$_=>uc} 'a'..'z';
    my $subset = $ha->(\%hash, 'f'..'k');
    is_deeply $subset, { map {$_=>uc} 'f'..'k' }
        or diag explain $subset;
    $subset->{i} = 9;
    is_deeply \%hash, { i=>9, map {$_=>uc} 'a'..'h','j'..'z' };
}

[download]

In reply to Re^8: Selecting Ranges of 2-Dimensional Data by haukex
in thread Selecting Ranges of 2-Dimensional Data by haukex

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