我可以通过快速扩展添加协议一致的协议吗?
- //Plain old protocol here
- protocol MyData {
- var myDataID: Int { get }
- }
我想使默认的MyData协议相当(只是比较ID)
- extension MyData : Equatable { }
但是我得到这个可爱的错误:
“Extension of protocol ‘MyData’ cannot have an inheritance clause”
我正在寻找的行为是符合Equatable(协议)的BananaData,因为它实现了MyData协议,该协议可以提供Equatable
- //This is the method to implement Equatable
- func ==(lhs: MyData,rhs: MyData) -> Bool {
- return lhs.myDataID == rhs.myDataID
- }
- struct BananaData: MyData {
- var myDataID: Int = 1
- }
- func checkEquatable(bananaOne: BananaData,bananaTwo: BananaData) {
- //This compiles,verifying that BananaData can be compared
- if bananaOne == bananaTwo { }
- //But BananaData is not convertible to Equatable,which is what I want
- let equatableBanana = bananaOne as Equatable
- //I don't get the additional operations added to Equatable (!=)
- if bananaOne != bananaTwo { } //Error
- }
由于错误消息说:协议的扩展不能有继承子句.相反,您可以使MyData协议在原始声明中从Equatable继承.
- protocol MyData: Equatable {
- var myDataID: Int { get }
- }
然后,可以扩展为符合MyData的类型添加一个==的实现:
- func == <T: MyData>(lhs: T,rhs: T) -> Bool {
- return lhs.myDataID == rhs.myDataID
- }
但是,我不会推荐这个!如果您添加更多属性到符合类型,则不会检查其属性是否相等.举个例子:
- struct SomeData: MyData {
- var myDataID: Int
- var myOtherData: String
- }
- let b1 = SomeData(myDataID: 1,myOtherData: "String1")
- let b2 = SomeData(myDataID: 1,myOtherData: "String2")
- b1 == b2 // true,although `myOtherData` properties aren't equal.
在上述情况下,您需要为SomeData重写==以获得正确的结果,从而使得接受MyData冗余的==.