On Fri, 17 Jul 2009 09:46:11 -0400, Don <nos...@nospam.com> wrote:
Steven Schveighoffer wrote:
On Fri, 17 Jul 2009 08:08:23 -0400, Don <nos...@nospam.com> wrote:
In this case, I think bearophile's right: it's just a problem with
range propagation of the ?: operator. I think the compiler should be
required to do the semantics analysis for single expressions. Not
more, not less.
Why? What is the benefit of keeping track of the range of integral
variables inside an expression, to eliminate a cast? I don't think
it's worth it. As far as I know, the ?: is the only expression where
this can happen. You will get cries of inconsistency when the compiler
doesn't allow:
ubyte foo(uint x)
{
if(x < 256)
return x;
return 0;
}
-Steve
Already happens. This works:
ubyte foo(uint n)
{
return true ? 255 : n;
}
And this fails:
ubyte boo(uint n)
{
if (true) return 255;
else return n;
}
Does that require range propogation? That is, when the compiler sees:
return true ? 255
does it even look at the type or range of the other branch?
Does this compile:
class C {}
ubyte foo(C n)
{
return true ? 255 : n;
}
(don't have the latest compiler installed yet, so I couldn't check it
myself)
I think the situation is different because the compiler isn't forced to
consider the other branch, it can be optimized out (I'm surprised it
doesn't do that in the general if(true) case anyways, even with
optimization turned off).
-Steve