How do I create an object that returns different values in different scalar contexts?

Question

I want to return a different value in string context and numeric context like $! does. I know I can find out whether I am in list or scalar context with wantarray, but is there any way in pure Perl to determine which scalar context I am in? I assume there is an answer in XS as well and I am willing to take that answer if there is no way do it in pure Perl.

score 13 · Accepted Answer · answered Apr 29 '09 at 00:49

13

Check out the Scalar::Util module, specifically the dualvar() function:

use Scalar::Util qw(dualvar);

my $scalar = dualvar 10, "Hello";
my $twelve = $scalar + 2;          # $twelve = 12
my $greeting = $scalar . " world"; # $greeting = "Hello world"

Scalar::Util is part of the core distribution, and should be avaliable anywhere you have Perl.

answered Apr 29 '09 at 00:49

Chris Lutz

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Thanks, that does exactly what I need. I really need to go through the Core again. There are too many good things I have forgotten/never knew. – Chas. Owens Apr 29 '09 at 01:50

score 3 · Answer 2 · answered May 02 '09 at 00:39

While I can propose cases when this would be useful (maybe Roman Numerals), you would be better off creating an object with an integer and a string attribute. Use the appropriate attribute in the appropriate context.

This gives you the added flexibility of being able to overload operations with 'use overload'. In a Roman Numerals example, dualvar will work until you want to add 2 roman numerals together.

How do I create an object that returns different values in different scalar contexts?

2 Answers2