Why we will use obj$func() often

[Mark Hahn]

My apologies.  I posted this to c.l.p. by accident.   I meant to post this
to Prothon-users.

"Mark Hahn" <mark at prothon.org> wrote in message
news:d2Uhc.22272$dZ1.1600 at fed1read04...
> "Michael Geary" <Mike at Geary.com> wrote ...
>
> >Does anyone have some sample code where obj$func() would be used?
> > (Apologies if I missed it.)
>
> There have been so many messages about delegation and binding since Greg
> originally posted his meowing cat message that it's hard to remember what
> the original problem was that Greg pointed out.  At that time Prothon had
no
> solution for the problem.  Now there is a released solution but it is
> incomplete and has broken the xor operator ( ^ ) (don't tell anyone
<grin>).
> I'll restate it here in my own way (this is copied from something I posted
> on comp.lang.py).
>
> Statement of problem (These are tested programs from released Python and
> Prothon:):
>
> # Python
>
> class klass:
>     def __init__(self):
>         self.me = 1
>     def func(self):
>         print "func1,self"+str(self.me),
>
> class klass2(klass):
>     def __init__(self):
>         self.me = 2
>     def func(self):
>         klass.func(self)        # delegation
>         print "func2,self"+str(self.me),
>
> inst = klass2()
> inst.func()    # prints  func1,self2   func2,self2
>
> # Directly translated to Prothon
>
> Klass = Object()
> with Klass:
>     .me = 0            # extra line
>     def .__init__():
>         .me = 1
>     def .func():
>         print "func1,self"+.me,
>
> Klass2 = Klass()
> with Klass2:
>     def .__init__():
>         .me = 2
>     def .func():
>         Klass.func()    # does not do what python does
>         print "func2,self"+.me,
>
> inst = Klass2()
> inst.func()    # prints  func1,self0  func2,self2
>
> As you can see, the call Klass.func() got the function func from the
object
> Klass and then called it on Klass using Klass as the target "self" instead
> of the instance "inst".  This is not what Python did and this is the
> problem.
>
> In Python the call klass.func() was different because Python knows that
> klass is a class and therefore obviously cannot be the target of call (an
> instance), so it made the programmer pass the instance self to use as a
> parameter.
>
> To fix this, we need to be able to specify in general, what the self
object
> is going to be during the execution of a function in Prothon (I call this
> choice of self "binding self to function" even though it's temporary
during
> execution).
>
> Greg's solution was to replace the period before the function name in
> klass.func() with a different symbol to indicate that the func is not
> supposed to be bound to klass as the syntax normally suggests (as in
> list.sort!()), but instead defaults to the current self.  My final scheme
is
> almost the same but instead of just defaulting to self, it specifically
> forces it to self (this may seem like a semantic difference, but don't say
> that to Greg <grin>).
>
> So now we have this solution.  Note that delegation to an ancestor
prototype
> (class in Python), is a common operation, especially in the __init__
> function:
>
> Klass = Object()
> with Klass:
>     def $__init__():
>         $me = 1
>     def $func():
>         print "func1,self"+$me,
>
> Klass2 = Klass()
> with Klass2:
>     def $__init__():
>         $me = 2
>     def $func():
>         Klass$func()        # voila!  problem fixed
>         print "func2,self"+$me,
>
> inst = Klass2()
> inst.func()    # prints  func1,self2   func2,self2
>
>
>
>
>