slint/sixtyfps_compiler/tests/syntax/basic/self_assign.60

SuperSimple := Rectangle {
    TouchArea {
        clicked => { root.x += 1px; }
    }
    TouchArea {
        clicked => { x += 1px; }
    }
    TouchArea {
        clicked => { 12 += 1; }
//                   ^error{Self assignement need to be done on a property}
    }
    TouchArea {
        clicked => { x += "string"; }
//                       ^error{Cannot convert string to length}
    }

    TouchArea {
        clicked => { doesnotexist += 24; }
//                   ^error{Unknown unqualified identifier 'doesnotexist'}
    }

}