rhai/doc/src/rust/getters-setters.md

Custom Type Getters and Setters

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A custom type can also expose members by registering get and/or set functions.

Getters and setters each take a &mut reference to the first parameter.

Getters and setters are disabled when the [no_object] feature is used.

Engine API	Description	Return Value of Function
register_get	register a getter	any
register_set	register a setter	none
register_get_set	short-hand to register both a getter and a setter	none
register_get_result	register a getter	Result<Dynamic, Box<EvalAltResult>>
register_set_result	register a setter	Result<(), Box<EvalAltResult>>

Cannot Override Object Maps

Getters and setters are only intended for [custom types].

Any getter or setter function registered for [object maps] is simply ignored because the get/set calls will be interpreted as properties on the [object maps].

Examples

#[derive(Clone)]
struct TestStruct {
    field: String
}

impl TestStruct {
    // Remember &mut must be used even for getters
    fn get_field(&mut self) -> String {
        self.field.clone()
    }

    fn set_field(&mut self, new_val: &str) {
        self.field = new_val.to_string();
    }

    fn new() -> Self {
        TestStruct { field: "hello" }
    }
}

let mut engine = Engine::new();

    engine
        .register_type::<TestStruct>()
        .register_get_set("xyz", TestStruct::get_field, TestStruct::set_field)
        .register_fn("new_ts", TestStruct::new);

let result = engine.eval::<String>(r#"let a = new_ts(); a.xyz = "42"; a.xyz"#)?;

println!("Answer: {}", result);                     // prints 42

IMPORTANT: Rhai does NOT support normal references (i.e. &T) as parameters.