Incomplete knowledge + all powerful casts = troubles

[Steven Schveighoffer]

On Mon, 19 Sep 2011 13:23:32 -0400, bearophile <bearophileHUGS at lycos.com>  
wrote:

> This is a simplified version of some older D code of mine.
> The cast is needed to convert int->uint:
>
>
> uint foo(T)(T x) if (is(T == uint)) {
>     uint ans = 0;
>     while (x >>= 1)
>         ans++;
>     return ans;
> }
> void bar(int x) {
>     auto xx = foo(cast(uint)x);
> }
> void main() {}
>
>
>
> I have "improved" it adding a nice "in" in the bar() signature. The code  
> compiles and runs still:
>
>
> uint foo(T)(T x) if (is(T == uint)) {
>     uint ans = 0;
>     while (x >>= 1)
>         ans++;
>     return ans;
> }
> void bar(in int x) {
>     auto xx = foo(cast(uint)x);
> }
> void main() {}
>
>
> Unfortunately now the code contains a small bug. The cast now converts  
> const(int)->uint, and foo() will modify a const value, that gives  
> undefined effects in D2.

While I agree D2 needs a const_cast, this code is still correct.  uints  
are passed by value, so it is fine what you did.

I'd say to avoid needing the cast, you should instead change bar to this:

auto xx = foo!uint(x);

which should work just fine, no cast needed.

-Steve