From: Eric Mahurin <eric_mahurin@...>
Date: 2005-09-09T07:05:00+09:00
Subject: Re: Lexical Casts with Ruby

--- Paul Brannan <pbrannan@atdesk.com> wrote:

> On Fri, Sep 09, 2005 at 03:49:59AM +0900, Eric Mahurin wrote:
> > class String
> >   def self.from(obj); obj.to_s; end
> >   def to(klass); klass.from_s(self); end
> > end
> > 
> > If you did this, then I guess you could consider this the
> > overhead for each class that other classes want to convert
> > to/from - String, Integer, Float, Array, etc.
> > 
> > I would think this more straight-forward approach would be
> more
> > likely accepted.
> 
> Would you be more amenable to a solution like:
> 
>   class Object
>     def to(type, *args, &block)
>       return send("to_#{type}", *args, &block)
>     end
> 
>     def to_String
>       return to_s
>     end
>   end
> 
>   class String
>     def to_Integer
>       return Integer(self)
>     end
> 
>     # etc.
>   end
> 
> This eliminates the global constant by using double-dispatch,
> plus
> retains the ability to convert to a non-class type (e.g.
> foo.to(Enumerable)).
> 
> Paul

Let's say you have some aribitrary class that you want to
convert to/from a string.  With the above, you'd put the
to-string method in this class and the from-string method in
String.  I think better encapsulation would be to put both of
these in this new aribitrary class.  To do it this way and
force the method names to have the class name in them, you'd do
this:

class Object
  def self.from(obj,*args,&block)
    send("from_#{self}".to_sym,obj,*args,&block)
  rescue
    obj.send("to_#{self}".to_sym,*args,&block)
  end
  def to(klass,*args,&block)
    send("to_#{klass}".to_sym,*args,&block)
  rescue
    klass.send("from_#{self.class}".to_sym,self,*args,&block)
  end
  def to_String
    to_s
  end
  def to_Integer
    to_i
  end
end


class Xyz
  def self.from_String(s,base=10)
    ... make a Xyz from s ...
  end
  def to_String(base=10)
    ... make a String from self ...
  end
end


Of course in the above, "klass" doesn't have to be a Class, but
it does need to respond to the right from_* method.

I'm not sure of the value of using from_String/to_String over
from_s/to_s.  I think you'll have just a few classes that
you'll  have many classes converting from/to them.  You'll
never be able to convert from one arbitrary class to another. 
Also, the above code is kind of ugly forming method names and
trying two different methods (not very duck-type like) - but I
could get over it.

Would this work with the non-class types you are talking about?




	
		
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