use v5.12;
use warnings;
use Test::More;
use Benchmark qw/cmpthese/;

my $AoH;

for my $n_rec (1, 10,100,1000) {
    say;
    say "=== num of records is: ",$n_rec;
    $AoH = create_data(1,$n_rec);
    is_deeply(
              [sort &list_join],
              [sort &slice_join],
             );

    cmpthese(-1, {
                  'list_join'  => \&list_join,
                  'slice_join' => \&slice_join,
                 }
            );

}

done_testing;

sub list_join {
    my %H;
    %H = (%H,%$_) for @$AoH;
    return keys %H;
}

sub slice_join {
    my %H;
    @H{keys %$_}=() for @$AoH;
    return keys %H;
}

sub create_data {
    my ( $density,$records ) = @_ ;

    my @AoH;
    push @AoH, { map { rand 100 <= $density ? ("$_" => $_) :() } "A".."ZZ" } for 1..$records;
    return \@AoH;
}