From: "Iñaki Baz Castillo" <ibc@...>
Date: 2008-05-01T23:13:57+09:00
Subject: Re: How to create "def method(item)= (value)" ?

El Jueves, 1 de Mayo de 2008, Ken Bloom escribió:
> On Wed, 30 Apr 2008 09:56:04 -0500, Iñaki Baz Castillo wrote:
> > 2008/4/30, Ken Bloom <kbloom@gmail.com>:
> >> def initialize
> >>   @params={}
> >>  end
> >>
> >>  def param
> >>   @params
> >>  end
> >
> > But I don't want that since it allows any self modification way (.strip!
> >  .chomp! ...) and I just want to allow []=
> >
> > Thanks.
>
> In that case, do as I wrote further on and have the param function return
> a proxy that edits the params array in only the ways you want.
>
> class ParamsProxy
>   def initialize hash
>     #thanks to duck typing hash can be an Array instead, if you'd like
>     @hash=hash
>   end
>   def [] key
>     #with .dup here, mutating operations on the returned value
>     #will not affect the values stored in the @hash
>     #note that even attr_reader isn't this careful about the
>     #objects that it returns, and so if you want behavior
>     #like attr_reader, then omit the .dup here
>     @hash[key].dup
>   end
>   def []= key,value
>     @hash[key]=value
>   end
> end
>
> class MyClass
>   def initialize
>     @params={}
>   end
>
>   def param
>     ParamsProxy.new @params
>   end
> end
>
>
> I presented this in rough outline before, without code, because there are
> many ways one could want to dress this up -- having some kind of
> validation code, or having the object.param[key]=value update something
> else entirely, or shoving the whole thing behind a nice attr_accessor-
> like interface. I don't have the time now to think through all of the
> possibilities involved to come up with a general solution, nor do I have
> a clear idea of exactly what your other constraints are. But start here,
> be creative, and let us know exactly what you do come up with.

Thanks a lot. Very useful information :)


-- 
Iñaki Baz Castillo