[Development] The future of smart pointers in Qt API

[Vitaly Fanaskov]

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