in reply to Re: Re: Space taken by a coderef
in thread Space taken by a coderef

Ahh, I see. In this case, Perl compiles the closure once and only needs one copy of the optree. It only has to attach to the lexical scope once for each unique closure created, so you'll have the cost of a scratchpad that holds $first and $second, as well as the cost of the lexical variables within the closure.

It wouldn't surprise me if this were slightly more efficient than a hash, but you'd probably need to get up above five or six member variables before it pays off. You'll save a little bit on accessors, though, but that's probably just the cost of the optrees, and you can avoid that if you're clever.

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Re4: Space taken by a coderef
by dragonchild (Archbishop) on Jan 19, 2002 at 01:28 UTC
    The cost of the lexicals within the closure (and the operations of assigning to them) can be avoided by using direct access to @_. *shrugs*

    How would I avoid the cost on accessors? What exactly is this optree you're talking about? Can I affect the optree after creating the closure?

    ------
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[reply]
      The optree is Perl's internal representation of your code -- bytecode, in Parrot terms. Closures are nice because they all share the same opcodes. (To simplify things perhaps past the point of correctness :), a cv, or code value, is a struct with a pointer to the optree for the function. There's also a pointer to the lexical scratchpad that holds enclosed variables.) The only difference is the lexical pad to which the closure is attached.

      If you had a dozen accessors, you could write a dozen subroutines with individual optrees, or you could autogenerate them and use 1/12th the memory with one shared optree and closures.

      If you want to modify the optree, you'll have to use the B:: modules and learn a lot more than I know at the moment, or have a lot of luck. :)

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