请在评论中查看错误消息:
interface Printable {}
class Book(val title: String) :Printable
fun bookPrint(b: Book?):String = "Title: " + b?.title
class Author(val name: String) :Printable
fun authorPrint(a: Author?):String = "Name: " + a?.name
// Unsupported: [modifier on parameter in function type]
// -------------vv
fun printIt(f: (in Printable?) -> String, a:Printable):String {
return "Unknown: " + f.invoke(null) +
"Known: " + f.invoke(a)
}
fun main(args: Array<String>) {
// Type Mismatch:
// Required: (Printable?) -> String
// Found: KFunction1<Book?,String>
// -------vvvvvvvvv
printIt(::bookPrint, Book("Storm Front"))
// -------vvvvvvvvvvv
printIt(::authorPrint, Author("Jim Butcher"))
}
关键点:
bookPrint()
并且authorPrint()
都需要一本空书/作者printIt()
需要采取其中任何一个功能。
所以,考虑“生产者扩展,消费者超级”我认为我的问题是我希望输入参数是协变的,当它被硬编码为逆变(“in”)时。
我有这个想法没有奏效:
// Unresolved reference: KFunction1
// --------------vvvvvvvvvv
fun htmlList2(f: KFunction1<Printable?,String>, a:Printable):String {
return "Unknown: " + f.invoke(null) +
"Known: " + f.invoke(a)
}