In Perl Parentheses are Optional (except when they are not!)
In Perl parentheses are optional in many cases, except when they are not! It doesn’t matter how much experience you have, sooner or later you will step into this problem, as I did today, and hence the need to remind to other developers this. I was writing a very simple and tiny line of code:ok ( 0 == grep { $_->authors == 0 } @publications , "There are no publications with no authors" );
The idea is that I’ve a list of
publication objects contained into @publications, and each object has a method named authors that return a list of author names. The test above should check that there are no publications without at least one author.
The above test is syntactically correct, but semantically wrong!
Perl refuses to do what I meant: Can't locate object method "authors" via package "There are no publications with no authors".
The error quickly reminds me about the problem.
I am so used to avoid using parentheses around operators, in this case grep, that I forget to use them even when the operator is used inside another function, in this case ok. Therefore, grep slurps everything after it, in particular @publications (what I meant) and "There are no ... with no authors" string (not what I meant)!
The solution is straightforward: add parentheses around grep so that Perl understands where the boundaries are.
ok ( 0 == grep( { $_->authors == 0 } @publications ), "There are no publications with no authors" );
And the test now runs as I expect and want.
What about Raku?
Somehow the above problem is less happening to me in Raku. In fact, in order to drop parentheses, you have to use the precedence dropper:, that triggers in my mind a kind of be careful from here on.