From: Sam McCall <tunah.usenet@...>
Date: 2004-09-09T13:20:07+09:00
Subject: Re: [RCR] Unified type conversion framework

gabriele renzi wrote:
> #is! is broken, because it relies on is_a? that is not powerful enough 
> to really express a type, but #as (or #to.. I mean, the proposed system) 
> is powerful enough to expres any kind of type, including your #is! :)
I think there needs to be a difference between implicit conversions (if 
there are any) and explicit conversions though:
"hello".can_be! String # ok
"hello".is! String # ok (maybe this is just an alias to #to, but i like 

                    # the clarity)
123.can_be! String # ok
123.is! String # raises
It's like the current difference between to_s and to_str, which seems a 
bit arbitrary. I'm not too unhappy with is_a here, a way to specify an 
interface rather than a class would be nice, but it doesn't seem to be a 
big problem for me anyway.

> The same is said for can_be? Sure, I could introduce a method in the 
> ConvTable that checks if a conversion path exists, but it won't work 
> for, say,
>  'ciao'.as Integer
> because even if a String -> Integer conversion path do exist, you still 
> have to check the whole string. So you end up needing #as again.
Hmm, ok. Maybe
def can_be? t
   self.as t
   true
rescue TypeError
   false
end
>> This might even be rdoc-able, if it was at the top of a method. It'd 
>> certainly make the ad-hoc documentation I write today executable.
> 
> 
> exacylt what I was thinking of. The IdeaSpace is limited, it seem ;)
:)
Type checking for parameters (along with identifier typos) is one of the 
few things that still irritates me, sometimes I think I'd be happier in 
a dynamic-except-for-function-parameters language ;-)
Sam