[Development] New Qt example development guideline and revamping examples

Giuseppe D'Angelo giuseppe.dangelo at kdab.com
Wed Jan 18 13:12:39 CET 2023

On 18/01/2023 10:51, Kimmo Leppälä via Development wrote:
> Also, the guideline is a living document in wiki and we would be happy 
> to hear feedback and proposals for it!

Here's a few considerations:

> Consider also compiling with the more strict warning flags and fix any issues they reveal. 

As history shows, this is not going to happen unless we enforce it. The 
cmake-magic macros that are used to build examples should set those more 
strict flags and enforce them (-Werror).

> Clang
>     Use -Weverything compiler parameter
> Visual Studio
>     Use /Wall compiler parameter

These aren't good recommendations. There's basically no code that 
survives those flags, incl. libc++/MS-STL own headers.

>     Prefer signal/slot connection with lambdas: https://doc.qt.io/qt-6/signalsandslots.html

All the contrary, do NOT do that, as it results in 200+ lines unnamed 
lambdas. Strongly prefer named slots. Keep the lambdas short and to the 
point. Do not use unnamed lambdas.

>     Check Qt Coding conventions: https://wiki.qt.io/Coding_Conventions

This shouldn't be "recommended" but mandatory. We must follow the same 
style in examples as we do in the rest of our code.

>     Consider using clazy plugin (comes also with Qt Creator): https://www.qt.io/blog/porting-from-qt-5-to-qt-6-using-clazy-checks

This should also be mandatory and enforced by CI.

> Add example application to correct category, for instance by adding '\meta category {Graphics & UI}' below '\examples'

Is there a list of categories to pick from?

>     Do not use QT_BEGIN_NAMESPACE ... QT_END_NAMESPACE for example types. This namespace is exclusively for types in the Qt libraries.

This is broken. How is one going to correctly forward declare Qt names 
in a namespaced build of Qt without using those macros? Is there perhaps 
a more comprehensive discussion regarding how to write examples that 
cope with namespaced Qt builds?

Thank you,
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

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