如何在Scala中将类方法作为参数传递 [英] How to pass a class method as a parameter in Scala

问题描述

假设我有一个带有一些方法的 C 类

Lets say I have a class C with some methods

def class C {
  def f1():Int = ...
  def f2():Int = ...
}

现在我想要一个接受两个 C 实例的方法，以及一个 C 的方法，但我不知道 f1、f2 的类型是什么，也不知道如何调用它们.我想它看起来像

Now I'd like a method that takes two instances of C, as well as a method of C, but I don't know what the types of f1, f2 are, nor how to invoke them. I'm thinking it would look something like

def cmp(first:C, second:C, t:() => Int): Boolean = {
  first.t < second.t
}

这抱怨 t 不是 C 的方法.当然必须有一种方法来表达这一点.

This complains that t is not a method of C. Surely there must be a way to express this.

推荐答案

def cmp(first:C, second:C, t: C => Int): Boolean = {
  t(first) < t(second)
}

那么……

val c1 = new C
val c2 = new C
cmp(c1, c2, _.f1())
cmp(c1, c2, _.f2())

这是使用匿名函数.最后两行相当于:

This is using anonymous functions. The last two lines are equivalent to:

cmp(c1, c2, {c: C => c.f1()})
cmp(c1, c2, {c: C => c.f2()})

除非您使用某种反射，否则您无法传递对方法本身的引用.

You can't pass a reference to a method per se unless you use some kind of reflection.

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