IReadOnlyList extensions

IReadOnlyListExtensions.fs

open System
open System.Collections.Generic

[<AutoOpen>]
module Extensions =
    type IReadOnlyList<'T> with
        static member Append(a : IReadOnlyList<'T>, b : IReadOnlyList<'T>) =
            { new IReadOnlyList<'T> with
                member this.Count = a.Count + b.Count
                member this.Item with get i = if i < a.Count then a.[i] else b.[i - a.Count]
                member this.GetEnumerator () = (seq { for i = 0 to this.Count - 1 do yield this.[i]}).GetEnumerator()
                member this.GetEnumerator () = this.GetEnumerator() :> System.Collections.IEnumerator }
        
        static member Init(count : int, func : int -> 'T) =
            { new IReadOnlyList<'T> with
                member this.Count = count
                member this.Item with get i = if 0 <= i && i < count then func i else raise (IndexOutOfRangeException())
                member this.GetEnumerator () = (seq { for i = 0 to this.Count - 1 do yield this.[i]}).GetEnumerator()
                member this.GetEnumerator () = this.GetEnumerator() :> System.Collections.IEnumerator }
        
        member this.ToArray() =
            let ary = Array.zeroCreate<'T> this.Count
            for i = 0 to this.Count - 1 do
                ary.[i] <- this.[i]
            ary