Re: Is it possible to write a sub that understand default variables ?

Using $_ as the default for a function that normally accepts a list is a bad idea since @a = (); display_thing(@a); would use $_, and that would break the expected behaviour.

However, if you want a function that accepts either zero or one argument, you could do that as follows (pre 5.10):

sub func {
   my $s = @_ ? $_[0] : $_;
   ...
}
[download]

And if you want to arg to be called $_ in your sub:

sub func {
   for (my $s = @_ ? $_[0] : $_) {
      ...
   }
}
[download]

This last one is particularly ugly. I only use it when the sub consists entirely of s/// statements.

Comment on Re: Is it possible to write a sub that understand default variables ? Select or Download Code

Replies are listed 'Best First'.
Re^2: Is it possible to write a sub that understand default variables ? by Corion (Patriarch) on Dec 24, 2007 at 17:37 UTC
I just tried "empty @a" against my solution. The `_` prototype forces scalar context on the first argument: `/opt/perl/bin/perl5.10.0 -M5.10.0 -e 'sub display(_){say $_[0]};@a=(); +display(@a);push@a,"x";display(@a)'` [download] Whether that is considered to be unintuitive or not depends on the user I guess	[reply] [d/l] [select]
Re^3: Is it possible to write a sub that understand default variables ? by ikegami (Patriarch) on Dec 24, 2007 at 18:36 UTC
No surprises there `>perl -le"@a=qw(A B C); print lc @a" 3` [download]	[reply] [d/l]