Scala：如何定义“通用”函数参数？(Scala: How to define “generic” function parameters?)

 我正在试图学习Scala，并在Haskell有一点经验。 对我而言奇怪的一件事是，Scala中的所有函数参数必须用Haskell不需要的类型注释。 为什么是这样？ 尝试把它作为一个更具体的例子：一个add函数是这样写的： 
 
def add(x:Double, y:Double) = x + y
 
 但是，这仅适用于双精度（同样，int也因为隐式类型转换而工作）。 但是如果要定义自己的类型定义自己的+运算符，该怎么办？ 你如何编写一个可以定义+运算符的任何类型的add函数？ 

I am trying to learn Scala now, with a little bit of experience in Haskell. One thing that stood out as odd to me is that all function parameters in Scala must be annotated with a type - something that Haskell does not require. Why is this? To try to put it as a more concrete example: an add function is written like this:
 
def add(x:Double, y:Double) = x + y
 
But, this only works for doubles(well, ints work too because of the implicit type conversion). But what if you want to define your own type that defines its own + operator. How would you write an add function which works for any type that defines a + operator?

原文：https://stackoverflow.com/questions/1252915