C++ overloaded operators and D

[via Digitalmars-d]

On Wednesday, 12 November 2014 at 21:17:42 UTC, IgorStepanov 
wrote:
> On Wednesday, 12 November 2014 at 20:49:42 UTC, Marc Schütz 
> wrote:
>> On Wednesday, 12 November 2014 at 19:32:32 UTC, IgorStepanov 
>> wrote:
>>> On Wednesday, 12 November 2014 at 14:41:17 UTC, Marc Schütz 
>>> wrote:
>>>> On Wednesday, 12 November 2014 at 11:43:36 UTC, IgorStepanov 
>>>> wrote:
>>>>> C++ and D provides different behaviour for operator 
>>>>> overloading.
>>>>> D has a opIndex + opIndexAssign overloads, and if we want 
>>>>> to map opIndex to operator[], we must to do something with 
>>>>> opIndexAssign.
>>>>
>>>> operator[] can be mapped to opIndex just fine, right? Only 
>>>> opIndexAssign wouldn't be accessible from C++ via an 
>>>> operator, but that's because the feature doesn't exist. We 
>>>> can still call it via its name opIndexAssign.
>>>>
>>>>> operator< and operator> can't be mapped to D. Same for 
>>>>> operator&.
>>>>
>>>> That's true. Maybe we can just live with pragma(mangle) for 
>>>> them, but use D's op... for all others?
>>>>
>>>>> Binary arithmetic operators can't be mapped to D, if them 
>>>>> implemented as static functions:
>>>>>
>>>>> Foo operator+(int a, Foo f); //unable to map it to D, 
>>>>> because static module-level Foo opAdd(int, Foo) will not 
>>>>> provide the same behaviour as operator+ in D.
>>>>> Thus: C++ and D overloaded operators should live in 
>>>>> different worlds.
>>>>
>>>> Can't we map both static and member operators to opBinary 
>>>> resp. opBinaryRight members in this case? How likely is it 
>>>> that both are defined on the C++ side, and if they are, how 
>>>> likely is it that they will behave differently?
>>>
>>> opBinary(Right) is a template-functions. You can't add 
>>> previous declaration for it to struct:
>>>
>>> //C++
>>> struct Foo
>>> {
>>>   Foo operator+(const Foo&);
>>> };
>>>
>>> Foo operator+(int, const Foo&);
>>>
>>> //D
>>> extern(C++)
>>> struct struct Foo
>>> {
>>>   Foo opBinary!"+"(const ref Foo); //???
>>
>> I see...
>>
>>> }
>>>
>>> Foo opBinary!"+"(int, const ref Foo); //???
>>
>> But this would of course be opBinaryRight, and inside struct 
>> Foo.
>
> What if
> Foo operator+(const Bar&, const Foo&);?
> Is it Foo.opBinaryRight, or Bar.opBinary, or both?

For a C++ class interfaced from D: opBinary() in whichever of the 
two classes it is defined.

For a D class interfaced from C++: choose one, preferably 
opBinary(), as it's the "natural" one.