在 Kotlin 中，抽象函数的默认参数值是否继承？

Question

在Kotlin中，您可以定义一个带有默认值的抽象函数。

是否会将此默认值传递给实现函数，而无需在每个实现中指定相同的默认参数？

Answer 1

(It's OK to ask and answer your own questions)

下面的代码确认默认值已传递给实现。

interface IParent {
    fun printSomething(argument: String = "default") // default val specified in interface
}

class Child : IParent {
    override fun printSomething(argument: String){ // no default val specified in impl.
        println(argument)
    }
}

Child().printSomething() // compiles successfully, and prints "default"

Answer 2

不仅没有"need to specify the same default parameter in each of the implementations"，甚至不允许

Overriding methods always use the same default parameter values as the base method. When overriding a method with default parameter values, the default parameter values must be omitted from the signature:
open class A {
    open fun foo(i: Int = 10) { /*...*/ }
}

class B : A() {
    override fun foo(i: Int) { /*...*/ }  // no default value allowed
}

求评论

I guess if we wanted a different default value for the implementing classes, we would need to either omit it from the parent or deal with it inside the method.

另一种选择是使其成为您可以覆盖的方法：

interface IParent {
    fun printSomething(argument: String = defaultArgument())

    fun defaultArgument(): String = "default"
}

class Child : IParent {
    override fun printSomething(argument: String){
        println(argument)
    }

    override fun defaultArgument(): String = "child default"
}

Child().printSomething() // prints "child default"

在 Kotlin 中，抽象函数的默认参数值是否继承？

In Kotlin, are default parameter values to abstract functions inherited?

kotlin

methods

default-value

abstraction