From: Eric Mahurin <eric_mahurin@...>
Date: 2005-08-26T02:11:22+09:00
Subject: Re: idea: klass.from_s(str)

--- "David A. Black" <dblack@wobblini.net> wrote:

> > The klass.from_s(str) form also offers a little more power.
>  If
> > you are dealing with an arbitrary class (possibly of
> another
> > object) and you want to convert a String to an object of
> that
> > class, you just call the from_s method of that class.  You
> > don't have to go figure out what the right String#to_*
> method
> > to call is based on the class (and violate duck typing).
> 
> Duck typing is irrelevant here.

I think an example is needed to demonstrate my point.  Say you
have a command line parser where you want to convert options
from String to the relavent class.  Somewhere in the
specification, you may specify the class that you want the
option to be.  With the String#to_* methods, you have to do
something like this:

def parse_option(klass,option)
  if klass.equal?(String)
    option
  elsif klass.equal?(Integer)
    option.to_i
  elsif klass.equal?(Float)
    option.to_f
  else
    raise("can't convert #{option} to #{klass}")
  end
end

With klass.from_s(str) methods, here is what you get:

def parse_option(klass,option)
  klass.from_s(option)
end

Which is duck-typed?

And like I said, in another message, we can still have this to
add more convienence:

class String
  def to(klass)
    klass.from_s(self)
  end
end



		
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