Range Types

[hunger]

Feature Description

I have been wondering whether we could have Ranges as types in Slint.

A range would be a integer or float value between an upper and a lower bound. I have been running into variables that have some valid range (e.g. a speedometer might go from 0 to 280 or a minute has between 0-59 seconds).

Exposing this range information in the type system could be very convenient for users and would also help doing UIs in our tooling.

Product Impact

No response

[ogoffart]

We could have range type.

strawman syntax:

struct Date {
   month: int#(1 -> 12),
   day: int#(1 -> 31),
}
//...
property <duration#(1min->60min)> foobar: 5min;

If the range is in the type, what should happen when converting from a non-range type and the thing is out of range?
Should the setter of the property return an error?

If this is only for the purpose of "hints" for the live preview data, then we may add hints instead as semantic "comments" in the code:

@range(1min, 60min)
in property <duration> foobar;

//....
struct Date {
   @range(1, 12) 
   month: int,
   @range(1, 31)
   day: int,
}

In which case, the range is not part of the type, but just an annotation to a property or field. And the range might not be "valid", it's just a hint for the live preview to set data.