[Development] Redesigning QML value types

Ulf Hermann ulf.hermann at qt.io
Wed Sep 21 18:45:16 CEST 2022

> Generally I feel that all the gritty details in what to do and what
> not do in qml to have efficient, compiled code, are more and more
> confusing. There is so much to consider and basically all the
> documentation about this is hidden in Qt blog posts.

Well, yes. All of this is 10 years late and we have to shoehorn it into 
an existing language with compatibility promises. So, some inconsistency 
cannot be avoided. I'm doing what I can to avoid confusion, though. The 
blog posts are in fact being transformed into regular documentation. It 
takes some time, though.

> Anyway I'd just like to note that, as far as I can remember, type
> annotation are currently not supported in lambdas (=> syntax).

Indeed not. Type annotations are mostly meant for methods of QML types, 
which cannot be phrased as arrow functions. The only other place where 
they might be beneficial is in inner functions inside bindings or 
methods. The compilers cannot generate efficient code to call those, 
yet. Therefore it doesn't make much sense to annotate them, yet. We'll 
get back to that when we get there. Help is always welcome, by the way.


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