property observer bug

NumberString.swift

class NumberString {
    var number = 0
    var string: String = "" {
        didSet { number = string.toInt()! }
    }
    
    init(foo: String) {
        string = foo  // Will NOT cause didSet
    }

    init(bar: String) {
        setString(bar)
    }

    func setString(foo: String) {
        string = foo  // Will cause didSet
    }
}

var foo = NumberString(foo: "123")  // number = 0
foo.string = "456"                  // number = 456
var bar = NumberString(bar: "789")  // number = 789

I understand. It's mismatch between "var is initialized" and "it's in initializer".
Currently, following condition takes priority.

They are only called when the property’s value is set outside of an initialization context.

I guess these comes from two different side "What is required before calling func in initializer?" and "When can property be observable?".
It's interesting.