From: "David A. Black" <dblack@...>
Date: 2005-08-26T00:36:35+09:00
Subject: Re: idea: klass.from_s(str)

Hi --

On Thu, 25 Aug 2005, Eric Mahurin wrote:

> I was thinking how in seems a little asymmetric that many
> classes have #to_s method, but when you want to make one of
> those objects from a String, you have to clutter the String
> class with yet another #to_* method.  So the String class gets
> the burden of all those #to_* methods.

I don't see that as a burden.  It seems to correspond precisely to
what's happening.

> Instead, what if we
> would have the convention that creating an object from a string
> would be a class method (for the class of that object) instead
> of another String#to_* method.  So, instead of these:
>
> String#to_i
> String#to_f
> String#to_sym
> String#to_<c> # where c is a abbreviation for the class
>
> you'd have these:
>
> Integer.from_s(str)
> Float.from_s(str)
> Symbol.from_s(str)
> klass.from_s(str)

That seems like at least an equal amount of clutter -- actually more,
since you've now got a receiver, method, and argument, where the
argument and the method name contain the same information (String-hood
in this case).  It also introduces a whole range of scenarios
involving wrong arguments.  I prefer simply sending a conversion
request to an object and getting its response.

> Maybe you'd even want to be able to convert from an inspect
> string:
>
> klass.from_inspect(str)
>
> I'm not saying that we should replace all obj.to_ methods with
> klass.from_ methods.  I'm just saying to make them come in
> pairs.  If you have a klass#to_* method, you should have a
> corresponding klass.from_* method if appropriate.  This would
> make your class more encapsulated, instead of having some of it
> in String (or whatever class you are converting from).

So you'd have:

Integer.from_f(1.0)
Integer.from_s("1")
Integer.from_nil(nil)
Integer.from_i(1)

instead of

1.0.to_i
"1".to_i
nil.to_i
1.to_i

I'm afraid it seems circuitous and verbose to me.


David

-- 
David A. Black
dblack@wobblini.net