Question

I’m passing some arguments to a function, one of which might be undefined.

$a = ($config->function(param('a'),'int'));

my module contains a function which looks like this:

sub function{                    
        my $self = $_[0];           
        my $t = $_[1];              
        my $type = $_[2];           
        print "$self,$t,$type<br/>";
}

I’ve tried with shift instead of the @_ syntax, but there’s no change.
The problem is that if $config->function is called with an undefined param('a') it prints like this:

MY_FUNC=HASH(0x206e9e0),name,
it seems that $t is being set to the value of what $type should be and the undef is being ignored completely.

Answer 1

The CGI param method is correctly returning an empty list in the case of an error. This is standard behaviour for Perl subroutines and methods, which return a false value in the case of an erorr.

As @mob says, an explicit return undef is wrong precisely because it returns a one-element list in list context. This is a true value and implies success, which would break a lot of code if it was changed

All you need to do is change your code to extract the parameter separately

my $param = param('a');
$config->function($param, 'int'));

or if you’re really keen to put the call in the parameter list then you can write

$config->function(scalar param('a'), 'int'));

or

$config->function(param('a') // undef, 'int'));