extern(C++) void f(int[4]* t);
Mangles as: void __cdecl f(int (* const)[4])
Where did that const come from?
This would logically be connected to a C++ function declared:
void f(int(*x)[4]);
Which mangles: void __cdecl f(int (*)[4])
I think it very unlikely that any C++ user would have functions:
void f(int(*const x)[4]);
Nobody uses *const in C++.
Comment #1 by dlang-bugzilla — 2017-07-02T16:53:44Z
Only occurs when targeting the MS toolchain (-m64 / -m32mscoff).
-m32mscoff:
mangled: ?f@@YAXQAY03H@Z
demangled: void __cdecl f(int (* const)[4])
-m64:
mangled: ?f@@YAXQEAY03H@Z
demangled: void __cdecl f(int (* __ptr64 const)[4])
Comment #3 by iamthewilsonator — 2019-06-11T14:16:19Z
This is the * const problem all over again.
Comment #4 by kinke — 2019-06-11T20:58:37Z
(In reply to Manu from comment #0)
> Nobody uses *const in C++.
Don't forget Microsoft; you've already reported a similar MS-specific issue a while back, with the C++ new operator or some other allocator IIRC.
Well, here we go again:
C++: short test27(int arg[6]); // or `int arg[]`, same thing
Win64: ?test27@@YAFQEAH@Z [short test27(int * const)]
Linux: _Z6test27Pi [test27(int *)]
I don't think this C++ function can be declared directly and portably in D anyway.
But due to this const-hack, it apparently works in higher dimensions: one can represent C++ `int p[][6]` as `int[6]* p` in D, and that does indeed work portably for both MSVC and Itanium.
https://github.com/dlang/dmd/blob/7538ed0125531d3a49ea6d2e266f7bae6e83556f/src/dmd/cppmanglewin.d#L282-L283:
> attention: D int[1][2]* arr mapped to C++ int arr[][2][1]; (because it's more typical situation)
> There is not way to map int C++ (*arr)[2][1] to D
Still, I think that special case is not worth it and more confusing than useful. It's been there since 2014 or longer: https://github.com/dlang/dmd/pull/3160
Comment #5 by turkeyman — 2019-06-28T00:31:14Z
I don't follow your examples:
C++:
void test(int arg[6]);
void test(int arg[]);
These are identical in C++, and they should mangle the same; with no size.
And yes, we see that MSVC has `* const` here. This is actually uninteresting, because there's no way to make a declaration like this in D. In C++, it's just a lame way to pass an un-sized array, and would almost always just use a pointer.
This is what's interesting:
C++:
void test(int (&arg)[6]);
void test(int (*arg)[6]);
These are interesting because they have meaningful D counterparts:
void test(ref int[6]);
void test(int[6]*);
These cases should be fixed in our mangler, they are useful functions that appear relatively often and are the proper way to pass static-arrays in C++.
Comment #6 by robert.schadek — 2024-12-13T18:46:15Z