英文:
Use generic parameterized with any type as function parameter
问题
I want the mutate function accepts both BoxOf<Food> and BoxOf<Fruit>.
interface Food
abstract class BoxOf<C : Food> {
val children: MutableList<C> = mutableListOf()
}
interface Fruit : Food
class Apple : Fruit
class Lemon : Fruit
class BoxOfFood : BoxOf<Food>()
class BoxOfFruit : BoxOf<Fruit>()
fun mutate(parent: BoxOf<Food>) {
parent.children.add(Apple())
parent.children.remove(Lemon())
}
fun test() {
mutate(BoxOfFood())
mutate(BoxOfFruit()) // Type mismatch: inferred type is BoxOfFruit but BoxOf<Food> was expected
}
Thanks in advance.
英文:
I want the mutate function accepts both BoxOf<Food> and BoxOf<Fruit>.
interface Food
abstract class BoxOf<C : Food> {
val children: MutableList<C> = mutableListOf()
}
interface Fruit : Food
class Apple : Fruit
class Lemon : Fruit
class BoxOfFood : BoxOf<Food>()
class BoxOfFruit : BoxOf<Fruit>()
fun mutate(parent: BoxOf<Food>) {
parent.children.add(Apple())
parent.children.remove(Lemon())
}
fun test() {
mutate(BoxOfFood())
mutate(BoxOfFruit()) // Type mismatch: inferred type is BoxOfFruit but BoxOf<Food> was expected
}
Thanks in advance
答案1
得分: 3
以下是翻译好的部分：
由于您想要为 mutate 提供不同种类的 BoxOf<T> 并将各种水果放入其中，它应该接受任何 Fruit 的“消费者”，这写作 BoxOf<in Fruit>：
fun mutate(parent: BoxOf<in Fruit>)
这允许您传递任何 T 是 Fruit 的超类型（也是 Food 的子类型，由于 BoxOf 的约束）的 BoxOf<T>。
英文:
Since you want to give mutate different kinds of BoxOf<T>, and put all kinds of fruits in it, it should take any "consumer" of Fruit, which is written BoxOf<in Fruit>:
fun mutate(parent: BoxOf<in Fruit>)
This allows you to pass any BoxOf<T> where T is a supertype of Fruit (and also a subtype of Food, due to the constraint of BoxOf).
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