Is opCast need, we have to!

[Jesse Phillips]

foobar Wrote:

> I still haven't seen one example of generic code that uses a generic conversion. I remain unconvinced about this point and would appreciate an example.
> this is however a minor point in the discussion (stylistic issue) so let's move on to the more important parts.

Good point. I don't have one from experience. I can build on your example:

class Elderly : Person { 
   Elderly to(Person p) {
      Adult adult = to!Adult(p);
      return new Elderly(adult); 
   }
}

The above would throw an exception if p was a Kid. Note that your solution does not provide compile time checking because you'd still need a dynamic cast to retrieve an Adult from your person.

Providing a generic abstraction so when someone does find a use is a major style of Phobos.

> That was just one example. Let's discuss another one from your list then:
> uint foo = -1; // remember that this can be a result of a long calculation
> should the above compile in your opinion? 

No, I think int to uint should not be implicit. Maybe there is a reason other than C inheritance, I'm sure bearophile has a feature request for it.

> http://ideone.com/ksQDV 

I have an account so I get 15sec of runtime:

http://ideone.com/9ZvNL

Ok, I'm surprised this is successful. So I made another test that fails on my local machine, but strangely enough, succeeds on ideone...

http://ideone.com/gOtYc

Any way this demonstration is showing an  issue with overflow. I have already stated that explicit casts do not solve this and got no disagreement from you.

> I understand what you mean about the confirmation dialog but as you said yourself above, I'm not asking for a confirmation dialog but rather using safer actions. 
> I think we agree on this. 

Yes, we do agree. What we don't agree on is the best way to make things safer.

I am saying that implicit casts are not bad when data is not being lost.
And to! is a good candidate for providing safe conversions (possible data lost but qualifiers remain).
And that mixing conversions that loose data with ones that transform it (class conversion) is not an issue.