[cxx-abi-dev] manglings for exception specifications in function types

[Richard Smith]

On 11 October 2016 at 14:11, Richard Smith <richardsmith at google.com> wrote:

> Under
>   http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0012r1.html
>
> the noexceptness of a function type is now part of the type. As a result,
> we need manglings for exception-specifications on function
> pointer/reference types:
>
> void f(void()) {}
> void f(void() noexcept) {} // ok, overload not redefinition
>
> (It's not clear to me whether or not this was also necessary prior to
> C++17 to handle dependent exception specifications that appear lexically
> within the parameter list of a function template, and actual implementation
> practice varies as to whether such exception specifications are SFINAEable.)
>
>
> In order to handle overloading/SFINAE on exception specifications in
> dependent cases, we need to be able to mangle not only "noexcept", but also
> "noexcept(expression)" and "throw(<types>)". Suggestion for manglings:
>
> <exception-spec> ::=
>   nx  -- non-throwing exception specification
>   nX <expression> E  -- computed (value-dependent) noexcept
>

Minor correction: this should be mangled if instantiation-dependent, not
only if value-dependent. It appears that SFINAE can happen here.

  tw <type>* E  -- throw (types)
> <function-type> ::= [<CV-qualifiers>] [<exception-spec>] [Dx] F [Y]
> <bare-function-type> [<ref-qualifier>] E
>
> In the case of throw(a, b, c), we could omit types that are neither
> instantiation-dependent nor pack expansions (if that omits all types, we
> can use the 'nx' mangling instead), since C++17 says you can't overload on
> the actual types in the dynamic exception specification, and we otherwise
> only need them to be present if they might result in a substitution failure.
>
> Thoughts?
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sourcerytools.com/pipermail/cxx-abi-dev/attachments/20161022/cb49053a/attachment.html>