QMetaType and QVariant

Session Summary

Look at qmetatype.h and see whether we understand what's there.

Session Owners

Thiago, Fabian

Notes

• Fabian: could use dispatcher a la QSlotObject to reduce number of function pointers in QMetaTypeInterface
  • Ulf: contributes a lot to binary size
  • but code checks the pointers to avoid calling a function
    • e.g.trivially copyable? → memcpy
  • but a lot of the later additions could use a dispatcher
    • Thiago: each pointer is also a relocation
      • Marc: could set a nullptr to indicate calling a global function for all the built-in types to reduce relocs even more

• Replace the lessThan with the spaceship function in the interface
• Use spaceship in the impl of the interface for built-in types

• Looking at flags:
  • ideas to reducenumber of flags:
    • for QWeakPointer<QObject>
      • backend for QPointer
    • plans exist to phase it out

• std::function use
  • currently leaks it because the destructor code may already have been unloaded on destruction of registry
    • use function_ref?

• MutableViewFunction
  • use in QML, Fabian and Ulf know

• compare(void*, void*) function returns QPartialOrdering:
  • Marc: can stay as-is until we start to deprecate QPartialOrdering (just another one of the ordering types, behaves the same)

• QPairVariantInterfaceImpl
  • used in associative containers?
    • investigate where it's used, remove if not used

• type helpers
  • is_Real_Gadget? Seriously?

• enum helper
  • used in QDebug, QTest, etc

• when do we need Q_DECLARE_METATYPE?1
  • Fabian: QueuedConnection needs it

Session stopped 40% into the header file.

If you have questions or knowledge of QMetaType, talk to Thiago and Fabian.