QtCS2018 Date Time

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Howard Hinnant's new civil calendar and timezone proposals have made it to the C++ 20 draft (N4750)

  • Not implemented yet in any C++ Standard Library

Time Zone

  • Why would we use this, if we have to keep our existing code?
    • Allows us to hook to a standard tzdb implementation without forcing an ICU dependency
    • Good for Windows (MS doesn't want us to use the registry DB anyway)
    • Good for iOS (no need for Apple's ICU-wrapper API)
  • Can it be used without exceptions?
  • We should add a backend for it when we can
    • Drop unneeded backends

Front-end API

  • What do we do for QDate and QTime?
    • We should add conversion API for the new types as soon as we can
    • QT_HAS_INCLUDE(<chrono>), like QDeadlineTimer does for std::chrono::duration and std::chrono::time_point
  • Is there anything missing in C++20 draft which would prevent a QDateTime refactor in the 2020s?
    • (Keeping QDateTime convenience API but replace the QDateTimePrivate backend)
    • Eddy is working with Howard to make sure everything is there
  • Compilers don't have this yet, but should have it in 2019 or early 2020
    • But we don't think we can reimplement QDateTime using date.h for Qt 6
    • Too close to call, regarding BC guarantees
  • Review QDateTime API:
    • Anything we want to deprecate anyway?
    • Anything that would be difficult to implement with date.h and we'd want to provide different API for?

Calendar systems

  • Didn't have enough time to discuss this
  • We have a contribution for QAbstractCalendar
    • We need a solution that enables code outside of Qt to implement their own calendars