SwiftUI Combine ObservableProperty

ObservableProperty.swift

import Combine

private var retainForever = [AnyCancellable]()

class ObservableProperty<T>: ObservableObject {
    @Published private var value: T

    init(initialValue: T) {
        self.value = initialValue
    }
    
    func set(_ value: T) {
        self.value = value
    }
    func get() -> T {
        return self.value
    }

    typealias ValueHandler = (_ value: T) -> Void
    typealias ChangeHandler = (_ newValue: T, _ previousValue: T) -> Void

    func observe(_ handler: @escaping ValueHandler) {
        let subscription = self.$value.sink(receiveValue: handler)
        retainForever.append(subscription)
    }

    func onChange(_ handler: @escaping ChangeHandler) {
        let subscription = self.$value.dropFirst().sink { (newValue) in
            handler(newValue, self.value)
        }
        retainForever.append(subscription)
    }
}