Thank you Corion, that was very helpful. In the meantime I have also discovered the source of my confusion. I made the (wrong) assumption that simply saying

      our @EXPORT = qw(function);
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means that Spiffy would export function into package two. Actually what I need to do is declare that package one is the base class package two, like this:

      use one -base;
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The problem is that package two lives in the same file as package one, and this causes a compiler error. The whole thing can be resolved by adding:

      import one;
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after the

      @two::ISA = qw(one);
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Thus the final program, and its output is:

#!/usr/bin/perl

package one;
use Class::Spiffy -base;
our @EXPORT = qw(function);
sub function { print "Function in package one\n" }

package two;
@two::ISA = qw(one);
import one;
print STDERR "Class::Spiffy version is ", $Class::Spiffy::VERSION, "\n
+";
print STDERR "Can two function? ",two->can('function'), "\n";
function();

__END__

cd /home/henry/dev/
/usr/bin/perl -w /home/henry/dev/spiffy_bug.pl 
Class::Spiffy version is 0.15
Can two function? CODE(0x814b738)
Function in package one

Compilation finished at Tue Feb 21 10:37:35
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Thanks to all who have tried to be helpful in solving this mystery.
Best wishes,
Henry Laxen