From: "David A. Black" <dblack@...>
Date: 2008-09-10T07:38:00+09:00
Subject: Re: How to access a method in the parent class

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Hi --

On Wed, 10 Sep 2008, James Coglan wrote:

> 2008/9/9 I=F1aki Baz Castillo <ibc@aliax.net>
>
>> Hi, I'll explain my problem with an example code:
>>
>> -----------------------
>> module M
>>        def hello
>>                puts "hello !!!"
>>                B.new
>>        end
>>
>>        class B
>>                def initialize
>>                        puts "B instance initialized !!!"
>>                        bye()   <--- ERROR !!!!
>>                end
>>        end
>> end
>>
>>
>> class A
>>        include M
>>
>>        def bye
>>                puts "bye !!!"
>>        end
>> end
>>
>>
>> a =3D A.new
>> a.hello
>> -----------------------
>>
>>
>> I want the following behaviour:
>>
>> irb> a.hello
>> =3D> "hello !!!"
>> =3D>  "B instance initialized !!!"
>> =3D> "bye !!!"
>>
>>
>> But the last bye() gives an error since, of course, "bye" is not defined=
 in
>> B
>> class, but in A class.
>>
>> I know that if it would be:
>> ------------------
>> module M
>>
>>        def hello
>>                puts "hello !!!"
>>                bye
>>        end
>>
>> end
>>
>> irb> a.hellp
>> ------------------
>> This works since "bye()" calls the "bye" method in class A. But this is =
not
>> my
>> case.
>>
>> How could I call A#bye method from M::B class?
>>
>> Thanks a lot.
>>
>
>
> To call a method from another class in the context of an instance of B, p=
ut
> this inside M::B#initialize:
>
> A.instance_method(:bye).bind(self).call()

That won't work here, because you'd need an instance of A (or a
subclass of A).

> Hard to tell from this code, seeing as how it does nothing apparently
> useful, but if you find yourself doing this it may be a sign that you nee=
d
> to rethink your design.

It definitely looks a bit inside-out: A requires that M exist, but A
is essentially trying to serve as a superclass for M::B. Sort of like
this:

module M
   def hello
     puts "hello !!!"
     B.new
   end
end

class A
   include M
   def bye
     puts "bye !!!"
   end
end

module M
   class B < A
     def initialize
       puts "B instance initialized !!!"
       bye
     end
   end
end

which works, but does indeed look like it would need some ironing out
in the design.


David

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