[Development] changing Q_GADGET

Simon Hausmann simon.hausmann at theqtcompany.com
Fri Nov 28 12:19:45 CET 2014


Monsieur Goffart did awesome work in the dev branch on allowing structures with 
Q_GADGET to have properties and invokable methods. This brings the macro to a 
much wider audience and I'd like to use this opportunity to propose a slight 
change to it that may be controversial:

The macros Q_OBJECT and Q_GADGET both - towards the end of their definition - 
change the member access permission level to "private". It's always been that 

I'd like to propose changing Q_GADGET to not change the access permission 
level, so that you can write

struct MyStructure
    Q_PROPERTY(int x MEMBER x)

    int x;

I feel that Q_GADGET has its primary use with structures and the default 
access level for those is public. I find it awkward that you currently have to 

structure MyStructure
    int x;

The proposed change would have two effects:

1) It makes any existing code that _relies_ on Q_GADGET turning to private 
suddenly expose members in structures.

2) On paper it breaks binary compatibility with MSVC, in the unlikely event 
that somebody 
    a) produces a DLL and cares about binary compatibility
    b) exposes bare structures
    c) relies on Q_GADGET turning access permission levels to private

I feel that the effects are negligible compared to the benefit of a better API.

What do you think?


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