Question

这是我的游乐场：

class A {

    required init() { // in order to use X() this init must be required
    }

}

class B<X: A> {

    required init() {
        X()
    }

}

class C<X: A, Y: B<X>> {

    init() {
        Y() // Error here: 'X' is not a subtype of 'A'
    }

}

C()

Swift有可能吗？我做错了什么？

更新

我真正想要的是这个（Playground与此代码崩溃）：

import UIKit
import CoreData

class MyEntity: NSManagedObject {}

class GenericCell<X: NSManagedObject>: UITableViewCell {

    func doSomething(entity: X) {}

}

class MyEntityCell: GenericCell<MyEntity> {}

class C<X: NSManagedObject, Y: GenericCell<X>>: UITableViewController {

    init() {
        super.init(nibName: nil, bundle: nil)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // here I should have Y = MyEntityCell
        tableView.registerClass(Y.self, forCellReuseIdentifier: "Cell")
    }

}

C<MyEntity, MyEntityCell>()

Answer 1

可能，你想要什么，不是你在做什么......请检查这个'示例'

class A {
    required init() {
    }
}

class B<X: A> {
    required init() {
        //X()
    }

}
class BB: B<A>{
    required init() {
        //B()
    }
}

class C<SomeUnknownTypeAlias, TypeAliasForGenericClassB: B<SomeUnknownTypeAlias>> {

    init() {
    }
    func foo(){
        dump(TypeAliasForGenericClassB)
    }
}

let c = C()
dump(c)
c.foo()
let cc = C<A,BB>()
dump(cc)
cc.foo()
/*
- C<A, B<A>> #0
- B<A> #0
- C<A, BB> #0
- BB #0
*/

甚至更简单，因为那里根本不需要init ..

class A {}
class B<X: A> {}
class BB: B<A>{}

class C<SomeUnknownTypeAlias, TypeAliasForGenericClassB: B<SomeUnknownTypeAlias>> {

    init() {
    }
    func foo(){
        dump(TypeAliasForGenericClassB)
    }
}

let c = C()
dump(c)
c.foo()
let cc = C<A,BB>()
dump(cc)
cc.foo()

甚至更通用，因为B没有X要求

class A {}
class B<X>{}
class BB: B<A>{}

class C<SomeUnknownTypeAlias, TypeAliasForGenericClassB: B<SomeUnknownTypeAlias>> {

    init() {
    }
    func foo(){
        dump(TypeAliasForGenericClassB)
    }
}
// here C type requirements must be specified!
let c = C<A,B<A>>()
dump(c)
c.foo()
let cc = C<A,BB>()
dump(cc)
cc.foo()

Swift嵌套泛型

1 个答案: