Question

Update

The apparent problem was only due to a typo in my sample script, as noted by @M42. The eval hid the error caused by doing a break without given. The error message in $@ is:

Can't "break" outside a given block

So the case is clear and there is no problem at all. Going to close the question.

Another Update

Seems a little inconsistent, though; warning in one case but not in the other:

$ perl5.12.4 -WE "eval { say 0; say 1 if last; say 2 }; warn if $@; say 3"
0
Can't "break" outside a given block at -e line 1.
        ...caught at -e line 1.
3

$ perl5.12.4 -WE "eval { say 0; say 1 if last; say 2 }; warn if $@; say 3"
0
Exiting eval via last at -e line 1.
Can't "last" outside a loop block at -e line 1.
        ...caught at -e line 1.
3

Same output for perl5.14.1.

Wondering why those aren’t compile-time errors anyway. They are syntax errors after all.

And the message says we can’t exit via last or break when the implementation proves we can – the program simply carries on. Should eval really catch such broken code? Just a user wondering …

Original post

In a code review, I just saw a copied/pasted given/when/break where the given/when was deleted and the break was left over. The code compiles and runs without warnings. Which led me to the question:

Does break have defined behaviour outside of given/when ?

I couldn’t find anything authoritative in perlsyn. And I can’t see what would be the break-rationale from the output of the following program:

use 5.010;
use strict;
use warnings;

sub bla {
    my @args = @_;
    eval {
        for ( @args ) {
            say;
            if ( $_ eq 'blub' ) {
                say '==> break';
                break;
            }
            say 'nach if';
        }
        say 'nach for';
    };
    say 'eval Ende';
    say 'sub Ende';
}

bla qw/ eins zwei blub drei /;

say for '-' x 40;

eval {
    say 'im eval';
    say '==> break';
    break:
    say 'immer noch im eval';
};
say 'nach dem eval';

Identical output with 5.10.1, 5.12.4 and 5.14.1. Note in the first example all of eval/for/if are skipped, whereas in the second example eval continues.

eins
nach if
zwei
nach if
blub
==> break
eval Ende
sub Ende
----------------------------------------
im eval
==> break
immer noch im eval
nach dem eval

So is it undefined behaviour? Or do you have any relevant doc pointers?

Answer 1

Put a semicolon instead of a colon after the break instruction

break;

With a colon it is considered as a label.