Json Provided type gens don't work with "with"

Question

Here is a snippet that demonstrates what I'll talk about well:

open FsCheck
open FsCheck.Gen
open FSharp.Data

type Test = JsonProvider<"""{"collection": [ { "Name": "Rob", "Age": 3 } ] } """>
let testGen () = 
  gen {
       let! name = Arb.generate<string>
       let! age  = Arb.generate<int>
       let colObj = Test.Collection(name, age)
       return Test.Root([|colObj|])
      }

let specialTestGen () = 
  gen {
       let! test = testGen ()
       let item = test.Collection.[0]
       let foo = item.Name
       let changedItem = {item with Name = "Chris"}
       return {test with test.collection = [|changedItem|]}
      }

I'm trying to make a gen with some fields gen'd constantly. I can assign out in to foo the collection instance's name, but for some reason I can't construct another slightly modified version of the stuct. It tells me item has no property called Name, when clearly on the line before it, it does. Can I not use the "with" syntax this these libraries for some reason?

Answer 1

Type providers can only provide ordinary .NET types right now, not F# records and discriminated unions. The {x with ...} syntax is only for F# records.