On 2017-04-07 06:40, Sergio Martins wrote: > Some time ago I documented the guidelines on passing by value vs > const-ref: > https://wiki.qt.io/API_Design_Principles#Passing_by_const-ref_vs._Passing_by_value > > But the reality is that passing small structs by value is not very > popular and Qt's API mostly passes them by const-ref. > > The guideline is very simple: > - If your type has a non-trivial copy-CTOR or non-trivial DTOR then pass > by const-ref, no matter how small it is, to avoid calling those methods. > *[1] > - If your type has trivial CTOR and trivial DTOR, pass by value if it's > small, otherwise const-ref. Small meaning <= 16 bytes. > > The idea is that by value allows the struct's members to be passed in > CPU registers, see [2] for extensive research.
Option 2: Teach C++ to choose automatically if such types should be passed by value or by const-reference. This has the benefit that it can DTRT even when TRT varies by platform. (Option 3: Add a template class that implements Option 2? Is this possible?) -- Matthew _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
