F＃中的最大/最小值类型(Maximum / minimum value of type in F#)

Unchecked.defaultof<'T>为任何类型生成默认值。 是否有这样一种通用函数来为任何类型生成最大值/最小值，其中最大/最小值的类型是有意义的？

编辑

回答John Palmer关于我认为它会有用的问题：我想创建下面的函数的“可变”版本：

let InternalArrDiffMax (s : 'T []) (diff : 'T -> 'T -> 'C) = s |> Array.mapi (fun i e -> [| for j in i + 1 .. s.Length - 1 -> diff e s.[j] |] |> Array.maxBy (fun n -> n)) |> Array.maxBy (fun e -> e)

由于我不能声明一个可变变量而没有给它赋值，我不认为还有其他方法可以做到这一点：

let InternalArrDiffMax (s : 'T []) (diffFun : 'T -> 'T -> 'C) = let mutable max : 'C = // Generic max of 'C if it makes sense for i in 0 .. s.Length - 1 do for j in i + 1 .. s.Length - 1 do let diff = diffFun s.[i] s.[j] if (i = 0 && j = 1) || max < diff then max <- diff max

这就是为什么我认为我需要一个通用的最大。

Unchecked.defaultof<'T> generates the default value for any type. Is there such a generic function to generate the maximum / minimum value for any type where the type having a maximum / minimum value makes sense?

EDIT

To answer John Palmer's question of where I think it would be useful: I want to create a "mutable" version of the below function:

let InternalArrDiffMax (s : 'T []) (diff : 'T -> 'T -> 'C) = s |> Array.mapi (fun i e -> [| for j in i + 1 .. s.Length - 1 -> diff e s.[j] |] |> Array.maxBy (fun n -> n)) |> Array.maxBy (fun e -> e)

Since I can't declare a mutable variable without assigning value to it, I don't think there is other way to do it than:

let InternalArrDiffMax (s : 'T []) (diffFun : 'T -> 'T -> 'C) = let mutable max : 'C = // Generic max of 'C if it makes sense for i in 0 .. s.Length - 1 do for j in i + 1 .. s.Length - 1 do let diff = diffFun s.[i] s.[j] if (i = 0 && j = 1) || max < diff then max <- diff max

Which is why I think I need a generic max.

最满意答案

如果你必须继续这条路线，那么总是有反思。 不过，我建议不要使用MaxValue作为带外或特殊价值。

let inline tryGetMaxValue< ^a> () = match typeof< ^a>.GetField("MaxValue") with | null -> None | fieldInfo -> fieldInfo.GetValue() |> unbox< ^a> |> Some let maxvi = tryGetMaxValue<int>() // val maxvi : int option = Some 2147483647 let maxvf : float option = tryGetMaxValue() // val maxvf : float option = Some 1.797693135e+308 let maxvs : string option = tryGetMaxValue() // val maxvs : string option = None

If you must proceed on this route, there's always Reflection. However, I would advise against use of MaxValue as an out-of-band or special value.

let inline tryGetMaxValue< ^a> () = match typeof< ^a>.GetField("MaxValue") with | null -> None | fieldInfo -> fieldInfo.GetValue() |> unbox< ^a> |> Some let maxvi = tryGetMaxValue<int>() // val maxvi : int option = Some 2147483647 let maxvf : float option = tryGetMaxValue() // val maxvf : float option = Some 1.797693135e+308 let maxvs : string option = tryGetMaxValue() // val maxvs : string option = None