[Development] The future of smart pointers in Qt API

Bogdan Vatra bogdan.vatra at kdab.com
Fri Jan 31 14:05:52 CET 2020


  It seem the community it's still pissed off on TQC, so I'm going to break the 
ice here :).
  I'll personally go with std::* (not only for smart ptrs but for everything 
else (e.g. containers), except QString of course). QPointer still needs to 
stay as there is nothing in std:: which we can use (unless it's not needed 
  Regarding the second issue, I'd like to have (const) references & shared 
ptrs only and to avoid raw pointers. 


În ziua de vineri, 31 ianuarie 2020, la 12:07:52 EET, Vitaly Fanaskov a scris:
> Hello everyone,
> We’ve been discussing for a while how Qt6 API can be improved with using 
> smart pointers. Recently we came into some conclusions and want to 
> discuss them with the community.
> Smart pointers are for sure much better to use than raw pointers for 
> many reasons. They manage lifetime automatically, show ownership 
> semantic, and make code safer. It’s planned to officially recommend them 
> to use in Qt6 API instead of raw pointers whenever this is possible. For 
> sure, it should only be a choice for newly designed API.
> But how to use them in the API and which way is preferable is still 
> unclear. There are two main options we have:
> 1) Use std::*  smart pointers as-is.
> 2) Add Qt-style wrappers around std::* smart pointers and move old 
> implementations of Qt smart pointers to the Qt5Compact module.
> Both options have pros and cons. It would be useful to hear your 
> thoughts on it. It’s worth mentioning that some other options, like 
> using Qt smart pointers as-is, were also discussed. They were found less 
> suitable, but feel free to share your opinion if you disagree.
> Another thing to discuss is whether we should use raw pointers in the 
> API at all or not. There are a few options again:
> 1) Yes
> 2) No. Use “modern” approaches instead (pass mandatory dependencies by 
> either reference or const reference when using smart pointers makes no 
> sense, use something optional-like or tuples to return extra data from 
> functions, and so on)
> 3) Mix 1 and 2.
> There are pros and cons for all options. Share your opinion once again, 
> please.
> If there are any related things to discuss, let’s do that in this thread.
> -- 
> Best Regards,
> Fanaskov Vitaly
> Senior Software Engineer
> The Qt Company / Qt Quick and Widgets Team
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