open System

open System.Collections

open System.Collections.Generic

open System.Linq

open System.Text

open System.Runtime.Serialization.Formatters

open System.IO

open System.Data

open System.ComponentModel.DataAnnotations

open System.Globalization

​

open Newtonsoft.Json

open Newtonsoft.Json.Linq

open Newtonsoft.Json.Converters

open Newtonsoft.Json.Serialization

​

// https://stackoverflow.com/questions/55919895/can-newtonsoft-json-net-deserialize-be-made-lazy-in-f

​

let jsonToStream(value:'T) =

    //https://stackoverflow.com/questions/48119433/how-serialize-to-stream-with-json-net-on-f/48120146?r=SearchResults#48120146

    let serializer = JsonSerializer.CreateDefault()

    let std = new IO.MemoryStream()

    (   use sw = new StreamWriter(std, new UTF8Encoding(false, true), 4096, true)

        use json = new JsonTextWriter(sw, CloseOutput = false)

        serializer.Serialize(json, value))

    std.Position <- 0L

    std

let jsonFromStream<'T>(stream : Stream) =

    Console.WriteLine(typeof<'T>) // Print incoming type for debugging purpose

    let serializer = JsonSerializer.CreateDefault()

    use rdr = new StreamReader(stream, Encoding.UTF8, true, 4096, true)

    use jrdr = new JsonTextReader(rdr, CloseInput = false)

    let res = serializer.Deserialize<'T>(jrdr)

    Console.WriteLine(res.GetType()) // Print outgoing type for debugging purpose

    res

​

let jsonSeqFromStream<'T>(stream : Stream) =

    seq {

        // Adapted from this answer https://stackoverflow.com/a/35298655

        // To https://stackoverflow.com/questions/35295220/newtonsoft-json-deserialize-into-primitive-type

        let serializer = JsonSerializer.CreateDefault()

        use rdr = new StreamReader(stream, Encoding.UTF8, true, 4096, true)

        use jrdr = new JsonTextReader(rdr, CloseInput = false)

        let inArray = ref false

        while jrdr.Read() do

            if (jrdr.TokenType = JsonToken.Comment) then

                ()

            elif (jrdr.TokenType = JsonToken.StartArray && not !inArray) then

                inArray := true

            elif (jrdr.TokenType = JsonToken.EndArray && !inArray) then

                inArray := false

            else

                let res = serializer.Deserialize<'T>(jrdr)

                yield res

    }

​

type someType (Id:string) =

    member x.Id = Id

​

let l = seq {1 .. 5 } |> Seq.map (fun i -> new someType(i.ToString()))

​

let stream = jsonToStream(l)

​

//let mySeq = jsonFromStream<someType seq>(stream)

​

let mySeq = jsonSeqFromStream<someType>(stream)

​

printfn "First pass through the sequence:"

​

mySeq |> Seq.iter (fun (s) -> printfn "%s" (JsonConvert.SerializeObject(s)))

​

printfn "Second pass through the sequence (should be empty):"

​

mySeq |> Seq.iter (fun (s) -> printfn "%s" (JsonConvert.SerializeObject(s)))

​