momoryleak.swift

class Thing {

    // retain cycle 
    lazy var wifi: Wifi = {
        return Wifi { state in
            self.onConnectionHandler(state: state)
        }
    }()

    // no retain cycle
    lazy var wifi: Wifi = {
        return Wifi { [weak self] state in
            self?.onConnectionHandler(state: state)
        }
    }()
}

// Wifi 
class Wifi {
    private let onConnectionHandler: (UIApplicationState) -> Void
    
    init(_ connectionBlock: @escaping (UIApplicationState) -> Void) {
        self.onConnectionHandler = connectionBlock
    }
}