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How to assign string "0" in short circuit

by nikhil.patil (Sexton)
on Feb 04, 2008 at 12:08 UTC ( #665938=perlquestion: print w/replies, xml ) Need Help??
nikhil.patil has asked for the wisdom of the Perl Monks concerning the following question:


In the following scenario:
sub function1 { $var = shift || "No argument"; print $var . "\n"; }
How do I make sure that a string value "0" is assigned to $var when the argument passed to the function is 0?

Currently, if 0 is passed to the function, it assigns "No argument" to the variable. I want "No argument" to be assigned only if there was no argument passed in the call to the function. Can I not use short circuit to do this??

Thanks in advance!

Replies are listed 'Best First'.
Re: How to assign string "0" in short circuit
by olus (Curate) on Feb 04, 2008 at 12:28 UTC
    sub function1 { my $var = (defined $_[0]) ? $_[0] : "No argument"; print $var . "\n"; }
Re: How to assign string "0" in short circuit
by poolpi (Hermit) on Feb 04, 2008 at 13:05 UTC
    sub function1 { my ($var) = @_? @_:'no arg'; print qq{$var\n}; } function1(0); function1('0'); function1('zero'); function1();
    Output: 0 0 zero no arg


    Update : 'no arg'
Re: How to assign string "0" in short circuit
by BrowserUk (Pope) on Feb 04, 2008 at 13:07 UTC
Re: How to assign string "0" in short circuit
by jwkrahn (Monsignor) on Feb 04, 2008 at 12:23 UTC
    Upgrade to Perl 5.10.0 and use the  // operator instead.
Re: How to assign string "0" in short circuit
by saberworks (Curate) on Feb 05, 2008 at 04:56 UTC
    None of the code shown so far matches the original. When you shift off @_, it actually removes the value, allowing you to use the rest of @_ at your leisure.
    #!/usr/bin/perl use warnings; use strict; sub function1 { my $var = defined $_[0] ? shift : 'No argument'; print "$var\n"; } function1('zero'); function1(0); function1('0'); function1(0e0); function1('foolio'); function1();
      Thank you all for your suggestions. Finally I used the following code to solve the problem:
      sub function1 { my $var = defined $_[0] ? shift : 'No argument'; print "$var\n"; }
      But I still wonder if we cannot assign string value "0" to a variable using short circuit.

      // works well, but that is in Perl 5.10.0. What if we have a situation like the following (in Perl 5.8.8), where we have multiple expressions involved in the short circuit in order of preference:
      my $var = $hash1{$name} || $hash2{$name} || $some_default_value;
      This will assign the default value to $var if say the key $name is not defined in %hash1 and is assigned a value 0 in %hash2. Is a if-elsif ladder or complex nested ternary operators the only way to solve this? Or may be this is the reason why they came up with // in Perl 5.10.0
        Short circuit operators always evaluate in boolean context. In boolean context there are only true and false. The string "0" and numberic 0 are, among others, false. But, 0 (or empty string) is defined. So you need to check for defined-ness to allow them. See True or False? A Quick Reference Guide.

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