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This is the unreleased documentation for the next version of Slint.
For up-to-date documentation, see here.

Type Conversions

Slint supports conversions between different types. Explicit conversions are required to make the UI description more robust, but implicit conversions are allowed between some types for convenience.

The following conversions are possible:

  • int can be converted implicitly to float and vice-versa. When converting from float to int, the value is truncated.
  • int and float can be converted implicitly to string
  • physical-length, relative-font-size, and length can be converted implicitly to each other only in context where the pixel ratio is known.
  • the units type (length, physical-length, duration, …) can’t be converted to numbers (float or int) but they can be divided by themselves to result in a number. Similarly, a number can be multiplied by one of these unit. The idea is that one would multiply by 1px or divide by 1px to do such conversions
  • The literal 0 can be converted to any of these types that have associated unit.
  • Struct types convert with another struct type if they have the same property names and their types can be converted. The source struct can have either missing properties, or extra properties. But not both.
  • Arrays generally don’t convert between each other. Array literals can be converted if the element types are convertible.
  • String can be converted to float by using the to-float function. That function returns 0 if the string isn’t a valid number. You can check with is-float() if the string contains a valid number
export component Example {
    // OK: int converts to string
    property<{a: string, b: int}> prop1: {a: 12, b: 12 };
    // OK: even if a is missing, it will just have the default value ("")
    property<{a: string, b: int}> prop2: { b: 12 };
    // OK: even if c is too many, it will be discarded
    property<{a: string, b: int}> prop3: { a: "x", b: 12, c: 42 };
    // ERROR: b is missing and c is extra, this doesn't compile, because it could be a typo.
    // property<{a: string, b: int}> prop4: { a: "x", c: 42 };


    property<string> xxx: "42.1";
    property<float> xxx1: xxx.to-float(); // 42.1
    property<bool> xxx2: xxx.is-float(); // true
    property<int> xxx3: 45.8; // 45
}
slint