scala - Parametric polymorphism in scala

Question

I'm trying to implement parametric polymorphism to devolve functions that have case matching statements that use asInstanceOf[]. I need to match the type of arguments to a classes in another package of the project which accepts parameters. I've tried this code:

def abc[A](x: A, i: Int): Any =
{
    x(i)
}

On running, I get an error saying A does not take parameters. How can I match A to few of the classes in project1.package1 folder? These classes are similar to an Array/Vector and x(i) returns ith element. Each class takes a different datatype (like Int, Double, String etc).

Answer 1

如果类接受参数，它们可能是Function1. 不幸的是，不是全部

所以你可以写：

def abc[A <: Function1[Int, _]](x: A, i: Int): Any = {
    x(i)
}

但这不适用于所有带参数的对象，例如案例类伴随对象。因此，为了解决这个问题，您可以使用结构类型。就像是：

 def abc[A <: {def apply(i: Int): Any } ](x: A, i: Int): Any = {
    x(i)
}

基本上我们在这里所做的是接受任何类型的子类型，该子类型有一个apply方法，Int即它需要一个Int参数。

应该注意的是，如果您尝试将输入类型从泛化Int到任意T