Scala中的隐式函数未按预期工作(Implicit function in Scala not working as expected)

 如果我定义了以下函数，它需要Long，并且我定义了下面的隐式函数，当我将Date传递给第一个函数并且一切按预期工作时，使用隐式函数： 
 
def millisToDays(in: Long): Int = (in / (1000L * 3600L * 24L)).toInt
implicit def dateToLong(d: Date) = d.getTime
println(millisToDays(new Date))
 
 但是对于下面的第二个例子，我在第三行得到编译器错误：“推断类型参数[Int]不符合方法mySum的类型参数bounds [t <：java.lang.Number]” 
 
def mySum[T <: Number](as: T*): Double = as.foldLeft(0d)(_ + _.doubleValue)
implicit def intToInteger(n: Int): Integer = new Integer(n.toInt)
var r = mySum(2, 3)
 
 我做错了什么？ 为什么不使用intToInteger隐式函数？ 
 
 我猜测问题是隐式函数不返回“T <：Number”，而是返回一个Integer，因此编译器无法猜测隐式函数实际上是否有用。 
 
 无论如何，我可以给编译器一个提示，它应该使用隐式函数？ 
 
 谢谢！ 蚂蚁 

If I define the following function which expects a Long, and I define the following implicit function, the implicit function is used when I pass a Date to the first function and everything works as expected:
 
def millisToDays(in: Long): Int = (in / (1000L * 3600L * 24L)).toInt
implicit def dateToLong(d: Date) = d.getTime
println(millisToDays(new Date))
 
But for the following second example, I get a compiler error on the third line: "inferred type arguments [Int] do not conform to method mySum's type parameter bounds [t <: java.lang.Number]"
 
def mySum[T <: Number](as: T*): Double = as.foldLeft(0d)(_ + _.doubleValue)
implicit def intToInteger(n: Int): Integer = new Integer(n.toInt)
var r = mySum(2, 3)
 
What have I done wrong? Why isn't the intToInteger implicit function being used?
 
I am guessing that the problem is that the implicit function does not return a "T <: Number", but rather an Integer, so the compiler can't guess that the implicit function is actually useful.
 
Is there anyway which I can give the compiler a hint that it should use the implicit function?
 
Thanks! Ant

原文：https://stackoverflow.com/questions/8718530