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

[evilrat]

On Wednesday, 15 December 2021 at 12:02:08 UTC, Jan wrote:
> On Wednesday, 15 December 2021 at 11:03:27 UTC, rikki 
> cattermole wrote:
>>
>> On 15/12/2021 11:54 PM, Jan wrote:
>>> On Wednesday, 15 December 2021 at 09:36:54 UTC, Jan wrote:
>>>> Unfortunately it's the "annoying little details" that I 
>>>> immediately bumped into.
>>> 
>>> Just another example: I just learned that linking against C++ 
>>> DLLs is quite limited. I ran into the issue that linking in 
>>> an external variable doesn't work (even though the mangled 
>>> name that D chooses is correct), because DLLs work 
>>> differently than static linking does
>>
>> Are you sure that on the shared library side it was marked as 
>> exported?
>>
>> If a symbol is not exported, there is no guarantee (nor reason 
>> to think) that it will be visible during runtime linking to 
>> said shared library/executable.
>>
>> This isn't unique to D, its just how linkers work.
>
> Yep, checked that. Even checked the .exp file and compared the 
> mangled name there with the mangled name that D tries to use, 
> they are the same.

You probably know this but just in case - unlike C++ in D 
variables by default have thread local storage, to link with C++ 
global variable you need to use __gshared storage modifier in D, 
it is similar to 'shared' variable that unlike 'shared' tells the 
compiler "I know how to synchronize it myself".

```d
module a;

struct Foo {}

extern(C++)
__gshared Foo globalFoo;
```