struct S {
    let x: Int
}

extension S {
    init(a: Int) {
        self.init(x:  a); print(x)
        self.init(x: -a); print(x)
    }
}

let s = S(a: 100)
print(s.x)

// output:
// 100
// -100
// -100

extension S {
    init(b: Int) {
        x = b
        x = b // error: immutable value 'self.x' may only be initialized once
              // fix-it: change 'let' to 'var' to make it mutable
    }
}

extension S {
    init(c: Int) {
        self.init(x: a)
        x = a // error: 'let' property 'x' may not be initialized directly; use "self.init(...)" or "self = ..." instead
        self.init(x: -a)
    }
}