Undeterred by the proliferation of 'lazy' modules on CPAN, I feel it's time to inflict my own lazy module on the world. Since I'm too lazy to pass around references and de-reference them all over the place, I've had to learn to pay very, very close attention to when I'm using an alias of a value, and when I'm using a copy of it. In particular, I've been twisting and stretching subroutine calls and fors to avoid copying. Now, however, I'm stuck. I'd like a subroutine that accepts a single scalar value as an argument, and returns a function that returns an arrayref to … err, that's confusing. I want a function prepend such that prepend($a)->($b) returns $return = [ $a, $b ], and that's easy to achieve; but I also want $return->[0] = 3 (say) to change $a, and that seems harder. I eventually came up with 
sub prepend {
    for ( @_ ) {
        return sub {
            return sub { \@_ }->($_, @_);
        };
    }
}

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Now, if I write my $return = prepend_to(my $a)->(my $b), then $return->[1] = 3 changes $b, but $return->[0] = 3 does not change $a. This confuses me, since it seems that $a is only ever getting passed around as part of a subroutine call or a for loop, neither of which should be making a copy.

The strange thing is, if I change the for invocation to for my $a ( @_ ) (and the $_ later to $a), then everything works just as I'd expect. My question is: Why? Does sub compile in the value of $_, but look in its pad for a named variable like $a; or is it something more subtle?

P.S. The ‘too lazy’ in the title refers to the fact that I know I could just do this my capturing a reference to $_[0] early on in prepend and then de-referencing it in the subroutine, but I'd rather avoid doing all that hard work by nesting subs 7 levels deep. :-)

In reply to Too lazy to be lazy by JadeNB

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