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Re^4: OOP: ->Coderef for calling Private Methods (possibilites?)

by LanX (Canon)
on Dec 13, 2008 at 19:47 UTC ( #730188=note: print w/ replies, xml ) Need Help??


in reply to Re^3: OOP: ->Coderef for calling Private Methods (possibilites?)
in thread OOP: Obj->Coderef for calling Private Methods

> $obj->$code_ref(...) is the same as $code_ref->( $obj, ... ) and that seems pretty clear from the documentation.

References ?


Comment on Re^4: OOP: ->Coderef for calling Private Methods (possibilites?)
Re^5: OOP: ->Coderef for calling Private Methods (possibilites?)
by ccn (Vicar) on Dec 13, 2008 at 19:57 UTC
    This? perlobj#Method-Invocation
    1. An object is simply a reference that happens to know which class it belongs to.
    2. A class is simply a package that happens to provide methods to deal with object references.
    3. A method is simply a subroutine that expects an object reference (or a package name, for class methods) as the first argument.

    ...

    Whatever is on the left side of the arrow, whether a reference or a class name, is passed to the method subroutine as its first argument.

      That doesn't describe the RHS of -> at all?

      Nevermind, I see what you're saying.

      Yes THIS could be better. it says:
      How does Perl know which package the subroutine is in? By 
      looking at the left side of the arrow, which must be either
      a package name or a reference to an object, i.e. something 
      that has been blessed to a package. Either way, that's the 
      package where Perl starts looking. If that package has no 
      subroutine with that name, Perl starts looking for it in 
      any base classes of that package, and so on.
      ...
      
      The right side of the arrow typically is the method name, 
      but a simple scalar variable containing either the method 
      name or a subroutine reference can also be used.
      

      If there was any paragraph saying something like

      $obj->$coderef(@paras) is equivalent to $coderef->($obj,@paras) "no matter if the RHS and the LHS have any package relation"!
      would be a much clearer definiton and avoiding the need to experiment. (well I'm not sure how to express the "no matter" part in clear English, but I hope the point is clear)

      Cheers Rolf

      UPDATED: Typo in code.

        > How does Perl know which package the subroutine is in?

        It concerns calling by name only. If perl has a reference to code it just executes it. There is no need to determine a package for the call. And the sub itself knows the package it belongs to.

Re^5: OOP: ->Coderef for calling Private Methods (possibilites?)
by ikegami (Pope) on Dec 13, 2008 at 20:01 UTC
    The second half of the documentation reads

    the right side is a method name or a simple scalar variable containing either the method name or a subroutine reference, and the left side must be either an object (a blessed reference) or a class name (that is, a package name). See perlobj.

    I don't see how it could be clearer that a reference is allowed.

      "either the method name or a subroutine reference",

      Till now, I haven't run any tests, but it's not clear to read if it's a subroutine reference to a method or just to any subroutine.

      some additional phrases and examples are missing!

      It's perfectly possible that perl might do a check if the coderef is in the STASH of the class.

      and I don't see why such a powerful feature should be hidden in 3 dispersed half-phrases in the perldocs.

      Cheers Rolf

        it's not clear to read if it's a subroutine reference to a method or just to any subroutine.

        There's no such things as methods. There are methods calls and subroutine calls.

        If you mean it's not clear whether the it's a method call or a subroutine call, what gives you the impression it can be anything but a method call?

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