my @s = '0000001' .. '1000000';

cmpthese -1,{
    d => q[ my @d = @s; ],
    c => q[ my @c = @s; $c[ $_ ] += 0 for 0 .. $#c; ],
    a => q[ my @a = @s; $_ += 0 for @a; ],
    b => q[ my @b = @s; my @new; push @new, $_ + 0 while defined( $_ = shift @b ) ],
};