Swift：如何在库中的基类中构建属性

Question

我需要在库中构建一个基类，但是库不知道这个属性。在这种情况下，我如何构建基类。 这是代码示例：

///Code in the library
open class BaseClass {
    // the problem is here. how I can set up such a property in the base class 
    // where the type of the property is not available in the base class.
    public var property: ThePropertyTypeThatThatLibraryDonotKnow 

    init(property: ThePropertyTypeThatThatLibraryDonotKnow)
}

///CodeIn the main app
class ThePropertyTypeThatThatLibraryDonotKnow {
     var someProperty: Int
}

///Usage of the BaseClass

/// 1 use the BaseClass directly
let property = ThePropertyTypeThatThatLibraryDonotKnow()
let object = BaseClass(property: property)

/// 2 subclass the BaseClass.
class SubClass: BaseClass {}
let property = ThePropertyTypeThatThatLibraryDonotKnow()
let object = SubClass(property: property)

有没有办法可以声明

property

基类。

Answer 1

有多种方法可以解决这个问题，但我可能采取的方法是使你的基类通用。

open class BaseClass<T> {
    public var prop: T

    public init(prop: T) {
        self.prop = prop
    }
}

现在在您的应用程序中，您可以创建通用基类的专用子类：

struct InternalType {
    let value: Int
}

final class SubClass: BaseClass<InternalType> {}
let instance = SubClass(prop: InternalType(value: 99))
print(instance.prop) //prints InternalType(value:99)
print(instance.prop.value) //prints 99

为了使泛型类型在子类中更有用，您可能需要定义一个协议并将泛型类型约束到它。

//Library
public protocol HasIntValue {
    var value: Int { get }
}

//Updated definition of BaseClass
open class BaseClass<T: HasIntValue> { ... }

//App
extension InternalType: HasIntValue {}
extension SubClass {
    func add(other: T) -> Int {
        return prop.value + other.value
    }
}

我建议阅读 Swift 的泛型类型。 Swift 编程语言是一个很好的起点：https://docs.swift.org/swift-book/documentation/the-swift-programming-language/generics/#Generic-Types