From: Brian Candler <b.candler@...>
Date: 2010-10-21T17:58:47+09:00
Subject: Re: scope when reopening method

Rahul Kumar wrote in post #956019:
> The second option of "when needed" wont work since My will call meth()
> at
> some point that i don't know. I would have liked to leave meth() blank
> so that callers can do what they want there.

Yes, so my suggested solution would be to pass arr at the time the 
object is instantiated:

   arr = []

   m = My.new(arr)   # <<< NOTE
   def m.meth(str)
     # access some other object in application scope
     @arr << str
     do_something str # call some method in my app
   end

i.e. you squirrel it away in an instance variable for later use.

> However, i had sort of hoped somehow the reopened method could access
> scope of the class that was reopening it. You have clearly explained
> that it is operating in the space of the class itself. So no magic can
> happen here :(

Well, the particular example you showed *can* be made to work, using 
define_method() instead of def. That doesn't open a new scope, and so 
you have a closure, i.e. access to all the local variables in the 
enclosing scope.

   arr = []

   m = My.new
   class <<m;self;end.class_eval do
     define_method(:meth) do |str|
       # access some other object in application scope
       arr << str
       puts str # call some method in my app
     end
   end
   m.meth "hello"
   puts arr.inspect

However I would consider this to be "advanced" ruby, and would advise 
against it unless it's really needed. There may be a simpler solution to 
the way you've designed your application.

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