Hi all
It sounds convenient to monitor change in property's value using property
observer.
But TSPL(The Swift Programming Language) talk little about property
observer. There
are some questions abouts property observer.
1) when `didSet` observer will call?
I assume it's fine that changing property's value in `didSet` observer.
class Foo {
var a: Int = 0 {
didSet {
print("didset")
a = a + 1
}
}
}
let foo = Foo()
foo.a = 4 // only output "didset" once
Why it don't cause infinite loop?
2) infinite loop
// this code snippet cause inifinite loop
class Foo {
var a: Int = 0 {
didSet {
b = a + 1
}
}
var b: Int = 1 {
didSet {
a = b - 1
}
}
}
let foo = Foo()
foo.a = 2
3) override property observer
class Base {
var a: Int = 0 {
didSet {
print("base didset")
}
}
}
class Child : Base {
override var a : Int {
didSet {
print("child didset")
}
}
}
let child = Child()
child.a = 2 // output "base didset" and "child didset"
let base = child as Base
base.a = 4 // still output "base didset" and "child didset"
Why overriding property observer still call parent's `didSet` observer?
--
Adel
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