Array Predicates

The array operations any and all test the elements of an array against a predicate expression.

Note: Array predicates are experimental and subject to change. Tracking issue: slint-ui/slint#12777 ↗.

Syntax

A predicate expression has the form (name) => condition. It binds name to a value and evaluates condition, which must be a bool. The name is in scope only inside condition.

Predicates are passed to the array operations any and all, which supply each element in turn as name:

• array.any((name) => condition) reads true if condition holds for at least one element.
• array.all((name) => condition) reads true if condition holds for every element.

The argument name is available only inside the predicate expression, and its type is inferred from the array element type.

any returns false for an empty array, while all returns true for an empty array.

Example

export component Example {
    in-out property<[int]> list-of-int: [1, 2, 3];

    out property <bool> contains-two: list-of-int.any((value) => value == 2);   // true
    out property <bool> all-positive: list-of-int.all((value) => value > 0);    // true
}

slint

Current Limitations

Predicates are the only form of closure in the Slint language, and they are only accepted as the argument of any and all. A predicate cannot be stored in a property, passed to a function or callback, or called directly. The predicate must be written inline in the call to any or all; passing a closure stored in a local variable is rejected with an error.