Add support for filtering and mapping models in `.slint` directly

[dilawar]

I have a property<[FooMsg]> msgs that stores list messages I want to display in different tabs. I am not maintaining different properties for each tab. I can do that if the answer here is a No. Each message FooMsg has a field called tag that determines the Tab of the message.

Inside a Tab, Here is a psedo code that I use to filter the messages and display them.

for msg[i] in root.msgs {
   if msg.tag == root.tag { 
      Text {
         text : msg.text;
         row: i;
       }
   }
}

I was hoping for something like (pseudo code):

for msg in root.msg.filter( |x| x.tag == root.tag) {
   Text { text: msg.text, row : i };
}

Note that the value of i will be different in the second case. The second case is suitable for generating a grid-layout because i will take values that increase by 1 at each step and there won't be gaps.

In short, I am looking for a filter like function for the array before I can iterate over it. Suggestions?

[tronical]

While this isn’t possible in pure Slint yet, you can do this if you provide your Mode from Rust and place it behind a FilterModel. Would that help?

[tronical]

FWIW it would be nice to be able to write a filter like in your example in pure Slint as well.

[ogoffart]

We just would need to find a good syntax for it.

// Like in rust
for xx in model.filter(|x| x.tag == root.tag) : Rectangle {
// like in JS
for xx in model.filter(x => x.tag == root.tag) : Rectangle {
// specialized syntax
for xx in model | #.tag == root.tag : Rectangle {

We also would probably need a map adapror syntax as well.
Maybe a sorting one too?

[tronical]

Right, and we'd need the map/filter/sort in C++ as well. This sounds very well doable. My order of preference in syntax is JS > Rust > Special ;-)

[dilawar]

While this isn’t possible in pure Slint yet, you can do this if you provide your Mode from Rust and place it behind a FilterModel. Would that help?

Thanks! This might just work 🥳 .

[dilawar]

I also think the JS syntax is easier on the eyes than Rust syntax (especially when you are also supporting JS and C++).

[dilawar]

While this isn’t possible in pure Slint yet, you can do this if you provide your Mode from Rust and place it behind a FilterModel. Would that help?

Thanks again for the suggestion @tronical. It worked! Not sure if I am using it the most efficiently but for now it solves my problem.

        // Connect msglist to slint Window.
        let msglist_app = ModelRc::new(FilterModel::new(self.msglist.clone(), |s| s.code == "App"));
        self.window.unwrap().set_msglist(msglist_app);

[tronical]

👍 We could leave this ticket open to track the ability to specify filters in .slint itself. If you're okay with that then I'll edit the title slightly to reflect the intent.

[dilawar]

@tronical Sounds good.

[jmgrosen]

Any other workarounds suggested for this? It seems like it makes maintaining the "one source of truth" that Slint seems to otherwise do pretty well break quickly without losing modularity.