F# first class generic function cheating

FSharpCheat1.fs

open System

type Test() =
    let f = fun x -> x
    member this.F with get() = f
    
let t = Test()
ignore (t.F "5")   // 1
// ignore (t.F 5)  // 2
Console.WriteLine(t.F.GetType().BaseType)

// writes:
// 1: Microsoft.FSharp.Core.FSharpFunc`2[System.String,System.String]
// 2: Microsoft.FSharp.Core.FSharpFunc`2[System.Int32,System.Int32]
// 1 and 2: error FS0001: This expression was expected to have type string but here has type int