No more implicit conversion real->complex?!

[Don Clugston]

Norbert Nemec wrote:
> I just notice that as of D 0.150, implicit conversion from
> real/imaginary to complex does not work any more. I could not make out
> the message containing the suggestion by Don Clugston, so I'm not sure
> about the rationale.
> 
> In any case: if this conversion does not work implicitely any more, I
> wonder whether I understand the rule which conversions do? real->complex
> is possible without ambiguities or loss of information. Why not make it
> implicit?

It's not 100% unambiguous, there are two possible conversions
     7.2 -> 7.2 + 0i
and 7.2 -> 7.2 - 0i.

OK, it's not a big deal. But the real problem is that with that implicit 
conversion in place, overload resolution is a real nuisance.

Consider
creal sin(creal c);
real sin(real x);

writefln( sin(3.2) );

Now, 3.2 is a double, so it tries to find sin(double).
This fails, so it tries implicit conversions.
Both sin(creal) and sin(real) are possible, so it's ambiguous, and
compilation will fail.
Up to now, the only way of overcoming this was to supply seperate 
functions for float, double, real, and creal arguments. This is clumsy, 
and becomes impractical once multiple arguments are used.

> I think this is an important issue: in numerics, mixing of real and
> complex values happens all the time, therefore it should be as simple as
> possible.

I agree. But the implicit conversions were actually making mixing of 
real and complex functions much more difficult. It would be good to have 
someone other than me seriously thinking about these issues, and gaining 
some experience with numerics in D.