Re: Tracking down the source of a new 5.10 warning

[ikegami]

Subs only capture the vars they think they need. They get it wrong in the case sub { eval '$x' }.

In older versions of Perl, the error was silent.

$ perl -wle'
    sub make {
        my ($x) = @_;
        return sub {
            eval q{$x};
        };
    }

    print make(123)->()
'
Use of uninitialized value in print at -e line 9.

In newer versions of Perl, the error still exists, but a warning issued.

$ perl -wle'
    sub make {
        my ($x) = @_;
        return sub {
            eval q{$x};
        };
    }

    print make(123)->()
'
Variable "$x" is not available at (eval 1) line 2.
Use of uninitialized value in print at -e line 9.

The solution is to add a reference to the variable that needs to be captured inside of the anon sub.

$ perl -wle'
    sub make {
        my ($x) = @_;
        return sub {
            $x if 0;      # <--- added
            eval q{$x};
        };
    }

    print make(123)->()
'
123