Re: Spotting an empty array as argument

To distinguish between no argument and an empty array, you can use the ;\@ prototype. It makes it impossible to specify more than one argument, though:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

sub mysay (;\@) {
    my ($arr) = @_;
    if (defined $arr) {
        print "$_\n" for @$arr;
    } else {
        print "$_\n";
    }
}

my @arr2 = qw( Two/1 Two/2 );
mysay(@arr2);

my @arr1 = qw( One );
mysay(@arr1);

$_ = "Don't show";
my @arr0;
mysay(@arr0);

$_ = "Underscore";
mysay();

# This doesn't compile.
# mysay(qw(a b c));
[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

Comment on Re: Spotting an empty array as argument Select or Download Code

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Re^2: Spotting an empty array as argument by Chuma (Scribe) on Mar 25, 2021 at 21:49 UTC
Neat! Although of course in this case I do need to specify more than one argument...	[reply]
Re^2: Spotting an empty array as argument by LanX (Saint) on Mar 25, 2021 at 22:08 UTC
> It makes it impossible to specify more than one argument, though: I think you are confusing `@` with `\@` . The former will swallow the whole list `DB<40> sub my_say (;\@$$$) { dd \@_ } DB<41> my_say @a [["a1", "a2", "a3"]] DB<42> my_say @a,$a [["a1", "a2", "a3"], "A"] DB<43> sub tst (@) { dd @_ } DB<44> tst @a ("a1", "a2", "a3") DB<45> tst @a,2 ("a1", "a2", "a3", 2)` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^3: Spotting an empty array as argument by choroba (Cardinal) on Mar 25, 2021 at 22:11 UTC
> I think you are confusing @ with \@. No, I mean what you can try by uncommenting the last line. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]
Re^4: Spotting an empty array as argument by LanX (Saint) on Mar 25, 2021 at 22:25 UTC
Oh, I see. I just experimented with the newer prototypes like `+` and `_` but it's still a PITA. :/ Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]