dmd 1.046 and 2.031 releases

[Steven Schveighoffer]

On Thu, 16 Jul 2009 08:49:14 -0400, bearophile <bearophileHUGS at lycos.com>  
wrote:

> I'm playing with the new D2 a bit, this comes from some real D1 code:
>
> void main(string[] args) {
>     int n = args.length;
>     ubyte m = (n <= 0 ? 0 : (n >= 255 ? 255 : n));
> }
>
> At compile-time the compiler says:
> temp.d(3): Error: cannot implicitly convert expression (n <= 0 ? 0 : n  
> >= 255 ? 255 : n) of type int to ubyte
>
> You have to add a silly cast:
>
> void main(string[] args) {
>     int n = args.length;
>     ubyte m = (n <= 0 ? 0 : (n >= 255 ? 255 : cast(ubyte)n));
> }
>
> In theory if the compiler gets a smarter such cast can be unnecessary.
>

I don't see how, doesn't this require semantic analysis to determine  
whether implicit casting is allowed?  I think you are asking too much of  
the compiler.  What if the expression was instead a function call, should  
the compiler look at the function source to determine whether it can fit  
in a ubyte?  Where do you draw the line?  I think the current behavior is  
fine.  The D1 code probably works not because the compiler is 'smarter'  
but because it blindly truncates data.

Perhaps if it were an optimization it could be implemented, but the result  
of an optimization cannot change the validity of the code...

In other words, it couldn't be a compiler feature, it would have to be  
part of the spec, which would mean all compilers must implement it.

BTW, I think cast is a perfect requirement here -- you are saying, yes I  
know the risks and I'm casting anyways.

-Steve