context-sensitivity for selfwritten functions

[tos]

Dear Monks,

some intrinsic functions as f.i. 'localtime' are contextsensitive.

How can i realize this behavior with my own functions ? How does my function know whether it has to return a scalar- or a list-value ? Is there something to do with overloading ?

thanks in advance and regards, tos

[rob_au]

In order to distinguish between scalar and list return contexts, take a look at the wantarray function - See perldoc -f wantarray).

This functionality has been expanded further in the Want module which provides a greater generalisation of return contexts including top level contexts such as void, scalar and list, lvalue subroutine context and referential contexts (such as scalar, hash, array, object and alike).

[l3nz]

An excellent example of context sensitivity is given in this trim() magic function example by our fellow saint japhy.

I think it shows all you need to build a context-sensitive function: the key, as you can see, is a defined wantarray.

[Abigail-II]

#!/usr/bin/perl

use strict;
use warnings;

sub func {
    my $context = wantarray;
    print  "VOID"   if not defined $context;
    return "SCALAR" if     defined $context && !$context;
    return "LIST"   if                          $context;
}

print "Context is: "; func (); print "\n";
print "Context is: ". func (); print "\n";
print "Context is: ", func (); print "\n";
 
__END__
Context is: VOID
Context is: SCALAR
Context is: LIST

Abigail