f# - 如何编写与 Array.sum 兼容的新类型？

Question

type Foo(...) =
    ...

let a = Array.create 10 (new Foo())

let sum = Array.sum a

Answer 1

您需要添加一些 sum 使用的成员进行计算的函数:

type Foo(value:int) = 
  member x.Value = value
  // Two members that are needed by 'Array.sum'
  static member (+) (a:Foo, b:Foo) = Foo(a.Value + b.Value)
  static member Zero = Foo(0)
  // Not needed for 'Array.sum', but allows 'Array.average'
  static member DivideByInt(a:Foo, n:int) = Foo(a.Value / n)

sum函数从 Zero 返回的值开始然后添加 Foo 的值使用重载 +运算符( average 然后将结果除以一个整数):

let a = Array.init 10 (fun n -> Foo(n)) 
let sum = Array.sum a 
sum.Value // Returns 45