guid parse errors can't be caught and handled at runtime

[dfields-msft]

The winrt::guid constructor that accepts a string calls abort() on failure instead of throwing an exception. This precludes the application from handling the error, e.g. to show a message to the user or fall back to default inputs. There is also no try_parse() function, so the guid parsing functionality of the library is limited to strings which are a priori known to be valid GUIDs.

[kennykerr]

Yes, these are constexpr constructors meant to be used with literals at compile time. If you want to do it at run time you can always use a function like CLSIDFromString.

[dfields-msft]

CLSIDFromString is quite clumsy and "un-modern" compared with the parsing constructor for winrt::guid. If the abort() were simply changed to a throw, it would be just as good for constexpr (perhaps better, since abort() itself isn't strictly constexpr), and also better suited for runtime use, which is available either way since constexpr functions are exposed for runtime use. What disadvantage is there to using throw instead?

[kennykerr]

I'm not really sure. If you can throw from a constexpr function and it still works just as well at compile-time then I have no problem with such a change. Note that abort was used (vs terminate) because only abort worked with Clang for some reason. So you'd have to validate that (a) exceptions work in general and (b) it works reliably at compile-time across both Clang and Visual C++.

[dfields-msft]

Yes, I've successfully used throw in constexpr with Clang and MSVC before, and the documentation suggests that this is normative (in that a constexpr branch which evaluates to a throw statement is malformed and will fail to compile, but that a constexpr function may contain a throw statement that is not evaluated for a given compile-time invocation without error). See:
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#note-50
https://en.cppreference.com/w/cpp/language/constexpr
https://en.cppreference.com/w/cpp/language/constant_expression