cxx-qt-lib: mirror PartialEq impls added in the previous commit

[yuknig]

so that QList operand may appear on either side of an equality comparison.

[codecov]

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✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (90d7b2c) to head (64e89d1).

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[ahayzen-kdab]

Looks good, a bit unfortunate that because the types are different we need this reversal.

I guess another simpler way could be instead to make a as_slice(&self) -> &[T] method like Vec has then you could do like &[1,2] == list.as_slice().

I note that when looking at Vec<T> against &[T] it only allows you to compare a vec to slice and not slice to vec ? Instead you can do as_slice() to cause a slice to slice comparison which then works

@yuknig So i wonder if we should do the same here, keep only the PartialEq you have in the previous change and then add as_slice(), this would then be consistent with how a Vec works in std i think ?

[yuknig]

@ahayzen-kdab I'm afraid we can't implement as_slice() for QList with Qt 5. As I understand the documentation, QList does not guarantee a contiguous memory layout like one in Vec. It might have something like linked list layout:

Note: QVector and QVarLengthArray both guarantee C-compatible array layout. QList does not. This might be important if your application must interface with a C API.

UPD: The lack of data() and constData() functions in QList in Qt 5 also hints that we should not rely on contiguity of the memory storage.

[ahayzen-kdab]

@ahayzen-kdab I'm afraid we can't implement as_slice() for QList with Qt 5. As I understand the documentation, QList does not guarantee a contiguous memory layout like one in Vec. It might have something like linked list layout:

Note: QVector and QVarLengthArray both guarantee C-compatible array layout. QList does not. This might be important if your application must interface with a C API.

UPD: The lack of data() and constData() functions in QList in Qt 5 also hints that we should not rely on contiguity of the memory storage.

@yuknig right in Qt 5 a Qt 6 QList is actually a QVector so likely put as_slice() if possible (?) only for Qt 6 to QList, and in theory would be added to QVector too. But tbh Qt 5 is EOL anyway so it's a matter of just keeping it building not blocking new features because of it so using the cfg flags like we do elsewhere is the route. Or whether we just ignore this feature entirely as Rust std doesn't tend to implement reverse PartialEq like this from what i can see ?

[yuknig]

Yes, I think I can adapt codebase on the client side codebase so that it compiles without this change.