I'm not sure what code you're using for this. The node you reference doesn't do what your node seems to be doing.
Anyway, I wrote this to verify the behavior you describe:
use Benchmark 'cmpthese';
my $str = 'a' x 1_000_000;
cmpthese( -2, { substr_lvalue => sub { substr_lvalue( "$str" ) },
substr_mod => sub { substr_mod( "$str" ) },
}
);
sub substr_lvalue {
substr( $_[0], 0, 1 ) = '' while $_[0];
return;
}
sub substr_mod {
substr( $_[0], 0, 1, '' ) while $_[0];
return;
}
Rate substr_lvalue substr_mod
substr_lvalue 2.58/s -- -50%
substr_mod 5.16/s 101% --
I don't have much to add beyond that. My first thought about this was that the lvalue case must allow something that the four argument case can't allow, but I hadn't figured out what that was when I read the reply from tye that laid it out.
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