Fixing the imaginary/complex mess

[Andrei Alexandrescu]

On 04/30/2009 02:20 PM, Don wrote:
> D currently allows some conversions between complex/imaginary types and
> real types, which are highly dubious.
>
> Given creal z, ireal y, these casts are legal:
> real x = cast(real)z;
> x = cast(real)y; // always sets x==0, regardless of the value of y.
> But I believe that should not be legal.
>
> For the first case, it should be written as: real x = z.re;
> (which is shorter and clearer), and the second case is probably a bug,
> and should be x = y.im; (unless the intention really was to set x=0!).
>
> By the same logic, we could have sqrt(-1)==0, since the real part is 0.
>
> The most important effect of disallowing these casts would be to fix a
> host of bugs and wierd behaviour. All the A op= B operations involve a
> cast to A. If those nonsensical casts become illegal, the nonsensical
> op= operations become illegal automatically.
>
> Eg, ireal y;
> y *= y; // mathematically nonsense, y*y is real, so can't be stored in a
> pure imaginary type!
>
> There are a few segfault/ICE bugs (eg 718, 2839) which involve
> int/=complex, an operation which never makes any sense anyway.
>
> I think we're just making problems for ourselves by allowing these
> useless operations. I think they should be killed.
> Does anyone object? (If not, I'll create a patch to do it; it's not very
> difficult).

Don, instead of this fix, could be at best phase everything built-in 
about complex out?

Thanks,

Andrei