No more implicit conversion real->complex?!

[Don Clugston]

kris wrote:
> Don Clugston wrote:
>> 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.
> 
> By this argument, if the overloaded types were char and long (instead of 
> creal & real) then D should not allow implicit conversion there?

I can't think of many examples where you have overloads of both char and 
long. But it's _extremely_ common for complex functions to be overloads 
of real functions. Let's not forget that the purpose of implicit 
conversions is for convenience. IMHO, real->creal fails to be 
convenient, given the D's simple lookup rules.