问题描述
考虑下面的例子
class ClassA {
func createAnInstanceOfAnotherClass() -> AnotherClass {
return AnotherClass()
}
func callMeA() {
}
}
class ClassB {
func createAnInstanceOfAnotherClass() -> AnotherClass {
return AnotherClass()
}
func callMeB() {
}
}
class AnotherClass {
func doSomethingAndReturn() {
return
}
}
class MethodChain {
func methodChaintest() {
ClassA()
.createAnInstanceOfAnotherClass()
.doSomethingAndReturn() //return to ClassA
.callMeA() // call classA callMe
ClassB()
.createAnInstanceOfAnotherClass()
.doSomethingAndReturn() // return to ClassB
.callMeB() // call ClassB callMe
}
}
AnotherClass 类是否有可能返回创建它的类的实例? 在这个例子中,我想在使用 ClassA 和 ClassB 的方法链接时使用类方法 doSomethingAndReturn,然后使用来自 ClassA 或 ClassB 的方法来构造方法链
解决方法
您可以使用类型参数 AnotherClass
使 Creator
泛型,该参数存储其创建者的类型。
class ClassA {
func createAnInstanceOfAnotherClass() -> AnotherClass<ClassA> {
return AnotherClass(creator: self)
}
func callMeA() {
}
}
class ClassB {
func createAnInstanceOfAnotherClass() -> AnotherClass<ClassB> {
return AnotherClass(creator: self)
}
func callMeB() {
}
}
class AnotherClass<Creator: AnyObject> {
// weak to avoid retain cycles!
private weak var creator: Creator?
init(creator: Creator) {
self.creator = creator
}
func doSomethingAndReturn() -> Creator {
// assuming you always do method chaining,// and not do something weird with the intermediate results,// this should be safe to unwrap forcefully
creator!
}
}