How to pass a class by (const) reference to C++

[Tim]

On Monday, 13 December 2021 at 15:21:19 UTC, Jan wrote:
> On Monday, 13 December 2021 at 13:02:50 UTC, Ola Fosheim 
> Grøstad wrote:
>> Yes, I wouldn't want to use it, maybe manual mangling is 
>> better, but still painful. ```const A&``` is so common in C++ 
>> API's that it really should be supported out-of-the-box.  All 
>> it takes is adding a deref-type-constructor to the D language 
>> spec, e.g. ```ref const(@deref(A))```
>
> I fully agree. This pattern is so common in C++, that I am 
> surprised D doesn't have a way to do this already. The whole 
> idea of linking against C++ is to interop easily, with little 
> friction and high performance. Needing to build any shims or 
> redesign the C++ side is very much contrary to this goal.
>
> Does anyone know whether such issues have been discussed 
> before? I can't imagine I'm the first one to run into this.

A similar issue about tail const classes has already been 
discussed:
https://digitalmars.com/d/archives/digitalmars/D/const_Class_is_mangled_as_Class_const_const_299139.html

I made a pull request, which changes the mangling to tail const 
for classes passed directly as parameter or return type, but now 
think this would break too much code: 
https://github.com/dlang/dmd/pull/13369
The proposal to add a deref-type-constructor, would also allow to 
have tail const classes.