Arrays 具有O（1）查找和O（1）切片的F#数组

我需要一个类似数组的数据结构，支持

a.[i]

在时间O（1）和

同样在时间O（1）中

O（1）不要求更新。实际上，我所需要的只是一个带有就地切片或子数组概念的常量数组

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当然，我可以从

数组

构造这样的东西，但是如果我可以使用一个已经存在的数组，我会更高兴。

基于此目的，.NET标准库有这样的类型。不幸的是，它没有方法

Item

和

GetSlice

，分别允许您使用

[x]

和

[x..y]

语法。但您可以添加一个扩展：

type System.ArraySegment<'T> with

    member this.Item(x) =
        if x < 0 || x >= this.Count then
            raise (System.IndexOutOfRangeException("Index was outside the bounds of the array segment."))
        this.Array.[x + this.Offset]

    member this.GetSlice(start: int option, finish : int option) =
        let start = defaultArg start 0
        let finish = defaultArg finish (this.Count - 1)
        if start < 0 || finish >= this.Count then
            raise (System.IndexOutOfRangeException("Index was outside the bounds of the array segment."))
        new ArraySegment<'T>(this.Array, this.Offset + start, finish - start + 1)

键入System.ArraySegment（this.Array，this.Offset+start，finish-start+1）

type System.ArraySegment<'T> with

    member this.Item(x) =
        if x < 0 || x >= this.Count then
            raise (System.IndexOutOfRangeException("Index was outside the bounds of the array segment."))
        this.Array.[x + this.Offset]

    member this.GetSlice(start: int option, finish : int option) =
        let start = defaultArg start 0
        let finish = defaultArg finish (this.Count - 1)
        if start < 0 || finish >= this.Count then
            raise (System.IndexOutOfRangeException("Index was outside the bounds of the array segment."))
        new ArraySegment<'T>(this.Array, this.Offset + start, finish - start + 1)