[Development] PSA: symbol visibility and export macros need to be re-thought for clang/libc++

[Giuseppe D'Angelo]

On 04/04/2025 17:44, Thiago Macieira wrote:
> 
> The conclusion from this is that, from the point of view of the C++ language,
> they*are*  different types, even if they have the same mangling and can (and
> are) passed across library boundaries in by value, by pointer, in containers,
> etc. The big problem here is that the C++ standard does not recognise shared
> libraries & DLLs exist, so this is an area that is underdeveloped. Despite
> being the mainstream.
> 
> IMNSHO, this needs to be addressed in the Standard, ahead of modules even.

I wouldn't hold my breath there. If we think that Clang's 
type_visibility attribute helps, we should instead ask GCC to implement 
the same, and start plastering our public APIs with it. At least this 
will give us some useful results in 2-3 years time, rather than 10-20.

(I'm still unsure about _how_ the attribute works, specifically how does 
it figure out the TU and thus the shared library in which to pin the 
RTTI information?)

My 2 c,
-- 
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - Trusted Software Excellence

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