[Development] QProperty and library coding guide

[Thiago Macieira]

On Friday, 24 July 2020 00:20:46 PDT Olivier Goffart wrote:
> You do not need to use the empty array everywhere: only in the helper type
> created by the Q_PRIVATE_QPROPERTY macro. And it can be conditioned on
> pre-c++20 GCC.

The problem is that it is in QObject and other Qt classes. That's why I meant 
"everywhere". See its warnings with -pedantic:

https://godbolt.org/z/cYbbG3

though of course it can be disabled:

https://godbolt.org/z/zdbePj

This feature is GCC's extension that was there prior to C99 Flexible Array 
Members (FAMs use x[] as a syntax, not x[0]). As an extension that has been 
superseded, it can disappear at any time. Though I'll grant you again that a 
future compiler that does disappear it is one that will support 
[[no_unique_address]].

In all, I think we have enough workarounds for this, for past compilers.

Can I suggest that we prepare at least two papers for the standard? One for 
the member-to-containing-object trick and the second for what QProperty really 
is: sub-scope of a class. We don't want a different this pointer, we just want 
to scope.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel DPG Cloud Engineering