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, and string can be converted to float with the to-float() member function. See Converting Between Numbers and Strings.
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.

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

Converting Between Numbers and Strings

int and float convert implicitly to string. To control how many digits appear in the result, use the to-fixed() and to-precision() member functions instead of the implicit conversion. To always use a dot as decimal separator regardless of the locale, use to-string-unlocalized().

For the other direction, convert a string to a number with the to-float() member function, and check whether a string holds a valid number with is-float().

All these conversions use the decimal separator of the current locale, which is exposed as Platform.decimal-separator and defaults to the dot (.). For example, in a German locale the decimal separator is the comma (,):

The float value 1.5 converts to the string "1,5".
"1,5".to-float() returns 1.5.
"1.5".is-float() returns false and "1.5".to-float() returns 0: only the locale’s decimal separator is recognized when parsing.

Number literals in .slint files always use the dot, regardless of the locale. See the translations guide for how the decimal separator is determined.