Re: Transitioning libgomp from C to C++ implementation

Am Samstag, dem 09.05.2026 um 14:21 +0100 schrieb Jonathan Wakely via Gcc:
> On Sat, 9 May 2026, 09:40 Christopher Bazley via Gcc, <[email protected]>
> wrote:
> 
> > 
> > 
> > This flaw in the design of C++ is also what necessitated the invention
> > of nullptr, which would otherwise be unnecessary. Had the purpose of
> > 'void *' not been misunderstood, nullptr could simply have been defined
> > as a macro: ((void *)0).
> 
> 
> No it couldn't.
> 
> This thread is getting more and more of topic, but defining nullptr as just
> a void* would not allow the useful property of overloading functions like
> unique_ptr::operator= on whether the argument is an actual pointer (which
> would replace the owned pointer, but is disallowed by plain assignment) or
> is the special nullptr value (which is allowed).
> 
> That is:
> 
> uptr = (void*)0; // error
> uptr = nullptr; // ok
> 
> I think you have an overly simplistic idea of why nullptr was added to C++,
> leading to an incorrect conclusion about it only being necessary because of
> C++ pointer conversion rules.
> 
> It exists for reasons related to template type deduction and overloading,
> not because void* isn't convertible to other pointer types.

This was indeed the reason given in the original paper why (void*)0 was
not used.  The other use cases make sense though.

Martin