Question

In the following anonymous subroutine declaration, Perl seems to be parsing it as an indirect method call, rather than as a subroutine:

use 5.010;
use strict;
use warnings;

sub proxy {
    my $new = shift;
    say "creating proxy: $new";
    sub :lvalue {
        say "running proxy: $new";
        tie my $ret, 'Some::Package', shift, $new;
        $ret
    }
}

say "before";
my $p1 = proxy '_value';
say "p1 declared: $p1";
my $p2 = proxy 'value';
say "p2 declared: $p2";

which prints:

before
creating proxy: _value
running proxy: _value
Can't locate object method "TIESCALAR" via package "Some::Package" ...

If a return or my $sub = is added right before sub :lvalue {..., then everything works properly, and it prints:

before
creating proxy: _value
p1 declared: CODE(0x4c7e6c)
creating proxy: value
p2 declared: CODE(0x1ea85e4)

It also works if the :lvalue attribute is removed from the subroutine (but of course that changes the functionality).

So my question is why is this happening? Is this a bug in Perl related to attributes on anonymous subroutines? Is it for some reason an expected behavior? If it is a bug, is it registered?

Answer 1

Because the beginning of a statement is a valid place to find a goto label, and so the bareword sub followed by a colon token is parsed as the label sub:, which is followed by lvalue BLOCK, which is parsed as indirect object syntax.

If you force the parser to look for a term by doing return sub : lvalue { ... } or my $foo = sub : lvalue { ... } it parses as intended.