From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-08-10T19:00:23+09:00
Subject: Re: ambiguity between local variable assignment and writter method

On Sat, Aug 10, 2002 at 07:07:11AM +0900, Tom Sawyer wrote:
> On Fri, 2002-08-09 at 15:37, Dave Thomas wrote:
> > The behavior of parent classes would vary if they were subclassed by
> > classes that defined specific accessors, which might be upsetting.
> 
> could you elaborate on that a touch more? perhaps a small example?
> 

This is how I see it:

class A
	def initialize(blah)
		@blah = blah
	end

	def amethod(*args)
		# do things with args
		puts "I don't expect anything special to happen in the next line"
		@blah = ...  # doesn't use accessor as there isn't one
	end
end

class B < A
	def blah=(thing)
		# do something with thing
		puts "Hey, doing things in self.blah=, which may be wrong!"
		@blah = ...
	end
end

obj = B.new
obj.amethod(...)  


# vim: ts=4:

@blah=... inside amethod, defined in class A, will use self.blah=, which
could be wrong if you really need low-level access to the attribute.
amethod expects @blah not to use an accessor, so you're changing the
behavior of things belonging to the superclass. This isn't as
if you were overloading a method, since there's no easy way to avoid
self.blah= being called...

One solution: each method using @attr=... would have to ignore accessors
defined in derived classes. This involves changing the way Ruby looks for
methods, but I don't think it would be that hard.
This would however make Ruby dirtier, and I don't quite think I'd like that :-|

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