[英]generic type conforming to a protocol in Swift
Is it possible to require that specific instantiations of generic types conform to a protocol in Swift? 是否有可能要求泛型类型的特定实例符合Swift中的协议?
For example, say I have a generic type called Thing<T>
. 例如,假设我有一个名为Thing<T>
的泛型类型。 I want Thing<Int>
to conform to a certain protocol, but not Thing<T>
. 我希望Thing<Int>
符合某个协议,但不符合Thing<T>
。
Well, it might not be too onerous, and it might be obvious enough that you've ignored it, but you could make a 'specific instantiation of a generic type' - as: 好吧,它可能不会太繁琐,而且你可能已经忽略了它,但你可以做一个“泛型类型的特定实例化” - 如下:
class ThingOfInt : Thing<Int>, SpecialIntProtocol {
// implement SpecialIntProtocol (if it isn't already
// implemented in an extension)
}
or with a bit more generality: 或者更具普遍性:
class IntThing<T:IntegerType> : MyThing<T>, SpecialIntProtocol {
}
In Swift 2.0 you can extend protocols and types 在Swift 2.0中,您可以扩展协议和类型
When you extend it you can add a generic where
constraints. 扩展它时,可以where
约束条件下添加泛型。 Only types that matches that rule will be able to use that functionality 只有符合该规则的类型才能使用该功能
Example : 示例 :
public struct Thing<T> {
let x: T
}
extension Thing where T : IntegerType {
func giveMeInt () -> T {
return x
}
}
let a = Thing<Int>(x: 10)
a.giveMeInt()
let b = Thing(x: 10.1)
//b.giveMeInt() // Error
This way you can add an extra functionality to Thing<Int>
type 这样,您可以为Thing<Int>
类型添加额外的功能
I don't know a way to conform to a protocol in the extension, but it doesn't make much sense. 我不知道在扩展中遵循协议的方法,但它没有多大意义。
Limitation: Generic where T :
can be used with protocols and classes, that's why we can't specify Int there 限制:通用where T :
可以与协议和类一起使用,这就是为什么我们不能在那里指定Int
You can do something like using the where
keyword and pass a condition afterwords. 你可以做一些事情,比如使用where
关键字并传递一个条件。 Saw this under Where Clauses section https://developer.apple.com/library/mac/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html#//apple_ref/doc/uid/TP40014097-CH26-XID_275 在Where子句部分下看到这一点https://developer.apple.com/library/mac/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html#//apple_ref/doc/uid/TP40014097-CH26-XID_275
class Thing<T : SomeProtocol where reflect(T).summary != "Int"> {
...
}
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