> On Oct 11, 2016, at 5:11 PM, Richard Smith <[email protected]> wrote:
>
> Under
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0012r1.html
> <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
> 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?
That seems reasonable to me. I don’t think we need to optimize the “throw (a,
b, c)” case: It’s deprecated anyway, and having all the types makes for nicer
demangling.
Daveed
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