I know that method lookups are cached, but I am quite certain (from the last time I read the documentation) that that cache is associated with the package STASH, rather than each object, since it logically applies to the class (package) and is shared between all objects of that class.

I would have to dig into the code to be sure, but the memory overhead for bless appears to be very minimal — once an SV has been upgraded high enough to carry any kind of magic, it also has a STASH pointer, and AV and HV structures are complex enough that they always have those fields.

Arrays in Perl do have considerably smaller overhead than hashes, although not a factor of 10. If you have a large number of some class of object, enough to cause memory usage problems, changing the internal representation to arrays and using constant to name the fields is likely to help. If encapsulation has been respected, this will require no changes outside of the object's implementation class.

> I know that method lookups are cached,

I remembered hearing people talking about this. That was the only possible theory left.

> but I am quite certain (from the last time I read the documentation) that that cache is associated with the package STASH, rather than each object, since it logically applies to the class (package) and is shared between all objects of that class.

Cool, that's what I needed to know! :)

> Arrays in Perl do have considerably smaller overhead than hashes, although not a factor of 10.

I did some tests for different sizes, yes it's not that dramatic - a 50% win is a very optimistic scenario.°

> changing the internal representation to arrays and using constant to name the fields is likely to help.

Well it's not my project anyway and some of my colleagues have weird strategies when it comes to optimization.

Personally I'm thinking rather in O() categories, and 50% best case wouldn't convince me to refactor.

I'd rather give Toby's suggestion for Insight-Out-Objects a shot.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

°) Though I'm not too sure if I got the Powershell and Windows right, since all the spared "keys" should cause a bigger impact. Will need to dig deeper. :)

but I am quite certain (from the last time I read the documentation) that that cache is associated with the package STASH, rather than each object, since it logically applies to the class (package) and is shared between all objects of that class.

That is the case.

$ perl -M5.010 -e'
   package Foo { sub f { } }
   package Bar { our @ISA = "Foo"; }
   say for keys %{ $::{"Bar::"} };
   say "---";
   Bar->f();
   say for keys %{ $::{"Bar::"} };
'
ISA
---
ISA
f
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