GetDUValue.fsx

open Microsoft.FSharp.Reflection


module MA =
    type A = { AStr: string}
    type B = { BInt: int}

    type private DU =
        | A of A
        | B of B

    type Wrapper =
        private { Items: DU list}
        with static member init() = { Items = List.Empty}

    let getSomethingFromDU a =
        FSharpValue.GetUnionFields(a, typeof<DU>, true)
        |> snd

    let getSomething a =
        a.Items |> List.map getSomethingFromDU

    let createA w = { w with Items = (A {AStr = "Hello"})::w.Items}
    let createB w = { w with Items = (B {BInt = 5})::w.Items}

module Tests =
    open MA
    let run() =
        Wrapper.init()
        |> createA
        |> createB
        |> getSomething
        |> printfn "%A"

Tests.run()