protocol BarProtocol {
    var bar: Int?  { get set }
}

protocol FooProtocol {
    var foo: BarProtocol? { get set }
}

struct TestProperty: FooProtocol {
    
    var foo: BarProtocol?
}

class TestClass {
    
    var property: FooProtocol? {
        didSet {
            debugPrint("didSet")
            
            doSomething()
        }
    }
    
    func doSomething() {
        property?.foo?.bar // causes didSet to be triggered, which causes an infinity loop
    }
}

let instance = TestClass()
instance.property = TestProperty()