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Re^2: A couple questions on Moose::MOP::Class

by John M. Dlugosz (Monsignor)
on May 03, 2011 at 04:47 UTC ( #902629=note: print w/ replies, xml ) Need Help??


in reply to Re: A couple questions on Moose::MOP::Class
in thread A couple questions on Moose::MOP::Class

Re Class::MOP::Method::Wrapped: Out of curiosity, does it gather all the before/after/around stuff into one thoughtful list, or does it just keep chaining things with more single-use wrappers?

And I was wondering... how does an 'after' method get called without having the wrapper show up in the call stack? If the original is chained to with a GOTO, it won't get control back again.

Moose and Class::MOP make a distinction between methods defined in your class, and functions imported from other modules.
Yea, that's what "no moose" and "autoclean" is all about. So, the method enumerator does the same thing as autoclean, and they work by comparing the name recorded in the function itself with the name it's being accessed under, to tell if it was not imported.

Let me see if I'm following... for code that's been generated or otherwise not created using the classic 'sub' at package level, it won't record that origin and would always look like it was imported, even for generated methods like the accessors. So what that passage was trying to say is that a fully-quallified name in the Sub::Name or the natural origin of the function is used to determine if it was imported. Right?

From reading Sub::Name, I thought that it simply records what you wanted in the same spot that a natural born sub does anyway. You talk about "B" and "stash" and other things not in my namespace, which makes me think now that the determination of the natural born name was not something it was originally meant to do. So Sub::Name is a newer thing and Carp et al. were updated to look at it, but defining a sub still doesn't populate that itself?

Re Welcome to the twisty maze: Thanks.


Comment on Re^2: A couple questions on Moose::MOP::Class
Re^3: A couple questions on Moose::MOP::Class
by stvn (Monsignor) on May 03, 2011 at 19:10 UTC
    Re Class::MOP::Method::Wrapped: Out of curiosity, does it gather all the before/after/around stuff into one thoughtful list, or does it just keep chaining things with more single-use wrappers?

    No, the Class::MOP::Method::Wrapped object keeps 3 ordered lists, one of befores, one of arounds and one of afters and it makes sure to apply them in the order you defined them. The docs actually go into a lot of detail about how this works.

    And I was wondering... how does an 'after' method get called without having the wrapper show up in the call stack?

    It does show up actually, they are named ":before", ":around" and ":after", here is a comment from the source explaining some of this:

    # NOTE: # the methods above used to be named like this: # ${pkg}::${method}:(before|after|around) # but this proved problematic when using one modifier # to wrap multiple methods (something which is likely # to happen pretty regularly IMO). So instead of naming # it like this, I have chosen to just name them purely # with their modifier names, like so: # :(before|after|around) # The fact is that in a stack trace, it will be fairly # evident from the context what method they are attached # to, and so don't need the fully qualified name.

    If the original is chained to with a GOTO, it won't get control back again.

    It isn't done with GOTO actually, for exactly that reason, it is all quite controlled. If you look at the source you will see the $_build_wrapped_method method which does much of the dirty work.

    o, the method enumerator does the same thing as autoclean, ...

    Yes, but the method enumerator did it long before autoclean existed and way before autoclean was stable/sane.

    Let me see if I'm following... for code that's been generated or otherwise not created using the classic 'sub' at package level, it won't record that origin and would always look like it was imported, even for generated methods like the accessors. So what that passage was trying to say is that a fully-quallified name in the Sub::Name or the natural origin of the function is used to determine if it was imported. Right?

    Yes, but Sub::Name alters the internal (C-level) structure of the CV data structure to basically add the fully-qualified name. It then appears just as if it was originally defined in that package.

    You talk about "B" and "stash" and other things not in my namespace, ...

    B is the "The Perl Compiler Backend", it is a way to access all the C-level data structures from Perl. The "stash" is the name for an element of those data structures, specifically the place where I go to find the actual fully-qualified name of the sub.

    ... which makes me think now that the determination of the natural born name was not something it was originally meant to do.

    Right, we had to get all sneaky and use XS to get at this stuff, it is not normally exposed in Perl.

    So Sub::Name is a newer thing and Carp et al. were updated to look at it, but defining a sub still doesn't populate that itself?

    No, Sub::Name alters the underly C-level structure such that when Carp gets to it,... it is just there. No changes had to be made to other modules.

    -stvn

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