develooper Front page | perl.perl5.porters | Postings from September 2023

Re: //= and ||= in subroutine signatures

Thread Previous | Thread Next
Dave Mitchell
September 3, 2023 09:32
Re: //= and ||= in subroutine signatures
Message ID:
On Sun, Sep 03, 2023 at 11:48:14AM +0300, Ivan Vorontsov wrote:
> With perl v5.38.0 I wrote a code similar to:
>     perl -E 'sub foo ($x, $y //= 42, $z) {} foo(1, undef, 3)'
> and got the error:
>     Mandatory parameter follows optional parameter at -e line 1, near "$z) "
> So //= and ||= mark a parameter as optional, but optional parameters
> must follow mandatory ones. Outside of signatures these operators check
> a value of a variable. A mandatory parameter can have undef or false
> value. If it is feasible, maybe these operators could be applied to
> mandatory parameters as well.

I don't see how that could work. It makes for an ambiguity.

You could create a parser rule which says that that if a mandatory
parameter follows a ||= parameter, then the ||= should be interpreted as
mandatory and vice versa:

    sub f1($x, $y ||= 1, $z)     {...}  # $y is mandatory
    sub f2($x, $y ||= 1, $z = 1) {...}  # $y is optional

but then this becomes ambiguous:

    sub f3($x, $y ||= 1)         {...}  # is $y optional or mandatory?

Please note that ash-trays are provided for the use of smokers,
whereas the floor is provided for the use of all patrons.
    -- Bill Royston

Thread Previous | Thread Next Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at | Group listing | About