Re: C++ throw() clause

[Jeffrey Walton]

On Sun, Aug 16, 2020 at 7:14 PM Bruno Haible <bruno@clisp.org> wrote:
>
> Hi Florian,
>
> > > clang (at least in version >= 4), in C++ mode, supports the 'throw
> > > ()' declaration on functions, and uses it to optimize try/catch
> > > statements at the caller site.
> >
> > I think throw() has been removed from C++20:
> >
> >   <http://eel.is/c++draft/except.spec>
> >   <https://en.cppreference.com/w/cpp/language/except_spec>
> >
> > So it will soon break again.
>
> Thanks for the heads-up. But g++ 10.2.0 still understands this
> "removed" syntax:
>
> ==================== nothrow.cc ====================
> extern int validate (int x) throw ();
> extern void err (int e);
>
> int foo (int x, int y)
> {
>   try { validate (x); } catch (int e) { err (e); }
>   try { validate (y); } catch (int e) { err (e); }
>   return x + y;
> }
> ====================================================
> $ g++ -O2 -S -std=c++20 -Wall nothrow.cc
> <no error, no warning>
>
> And glibc/misc/sys/cdefs.h has not been updated yet. Is it certain
> that GCC and the GCC compatible compilers (clang, icc, etc.) will
> continue to support 'throw ()'?

Exception specifications have been deprecated for about a decade.
Prior to deprecation they fell out of favor and were not recommended.
Also see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3051.html.

About the only place I see them in modern software is
'noexcept(false)' when a destructor throws.

Jeff