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Re: Problems with PR 21210

Mark Mitchell wrote:
> Gabriel Dos Reis wrote:
>> Mark Mitchell <> writes:
>>   template<class T>
>>    inline complex<T>    make_std_complex(T __complex__ z)
>>    {
>>       return complex<T>(__real__ z, __imag__ z);
>>    }
>> has zero abstraction penalty. 
>> I'm very reluctant to additions of constructors.
> That's OK with me -- if you're willing to accept the fact that this will
> silently change the meaning of:
>   __complex__ double c99_cd;
>   complex<double> cpp_cd(c99_cd);
> I just want to make sure that you're aware that what you're suggesting
> will change that; it will now simply copy the real part, and ignore the
> imaginary part.

I suspect I won't be the only person to say this, but if this change is
made it should be documented VERY, VERY CLEARLY. I have personally
worked on code where both __complex__ double and complex<double> and the
exact above notation was moved to convert one to the other, and I'm sure
I'm not the only person (in particular because it was believed, I
believe not entirely without reason, that __complex__ was move efficent).


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