From: Robert Klemme <shortcutter@...>
Date: 2007-06-02T04:45:20+09:00
Subject: Re: nested methods don't really exist?!

On 01.06.2007 14:36, Artur Merke wrote:
> Hi,
> 
> I've just encountered somehow strange (for me) behavior of nested
> methods in ruby:
> 
> class A
>   def a
>     def b
>       print "bbb"
>     end
>   end
> 
>   def c
>     b
>   end
> end
> 
> irb(main):013:0> A.new.c
> bbb=> nil
> 
> class A
>   def b
>     print "BBB"
>   end
> end
> irb(main):019:0> A.new.c
> BBB=> nil
> 
> my first thought was that method/function 'b' would be local to
> method 'a' in class A (like it would be in Pascal). But this is of
> course not
> the case, as the above example shows.
> 
> Is suppose that method 'a' (re)defines  method 'b' every time it is
> called, therefore  using nested methods doesn't seem to be a
> good idea in ruby (better readability but much worse performance, esp.
> when 'b' isn't a oneliner)
> 
> 
> any comments?

You're right on.  I think that nested methods are a bad thing to have 
especially since invocation of an instance method has side effects on 
all instances:

irb(main):001:0> class Foo
irb(main):002:1>   def a
irb(main):003:2>     def b; 1; end
irb(main):004:2>     2
irb(main):005:2>   end
irb(main):006:1> end
=> nil
irb(main):007:0> f=Foo.new
=> #<Foo:0x7ff87288>
irb(main):008:0> f.b rescue "no"
=> "no"
irb(main):009:0> f.a
=> 2
irb(main):010:0> f.b rescue "no"
=> 1
irb(main):011:0>
irb(main):012:0* Foo.new.b rescue "no"
=> 1
irb(main):013:0>

#b is defined only after #a has been invoked at least once.  I cannot 
think of a scenario where you would want this behavior.

Kind regards

	robert