QtCS2024 Error handling

Session Owners

Volker Hilsheimer Note taker: Thiago

Notes

Intro: we already have too many attempts at this, going back at least as far back as 2017.

Volker's proposal:

• use the C++17-compatible full implementation by Sy Brand at https://github.com/tartanllama/expected
  • Licence: CC0 (QtC legal needs to confirm it's ok to use even for commercial, but Thiago thinks it is [but he isn't a lawyer])
  • Includes things that even most of Standard Library implementations don't yet
• import into Qt
• use it internally

Should we use it in public API?

• If we do, then we can't switch to std::expected (C++23) before at least Qt 7.0
• It becomes part of our ABI
• Shouldn't be named q23::expected because it conveys the wrong message
• Do we need to use it in public API?
  • No, we don't need it
  • But it's very useful for that; the type is designed for use in interface boundaries
• Suggestion:
  • Use it internally first so we gain experience with its issues and how to use it
  • Then, later, make it public to use it

Alternatives:

• Boost LEAF
• Boost Outcome