module Colour = struct
  type t = { red : int; green : int; blue : int } [@@fieldglass generate]
end

module Legacy = struct
  type t = { value : string } [@@lens generate]
end

let () =
  let colour = Colour.{ red = 3; green = 4; blue = 5 } in
  assert (Colour.red colour = 3);
  assert (Colour.green colour = 4);
  assert (Legacy.value Legacy.{ value = "grey" } = "grey")

module Box = struct
  type 'a t = { contents : 'a } [@@fieldglass generate]
end

module Mutable = struct
  type t = { mutable count : int; label : string } [@@fieldglass generate]
end

let () =
  let original = Colour.{ red = 3; green = 4; blue = 5 } in
  assert (Colour.set_red 8 original = Colour.{ red = 8; green = 4; blue = 5 });
  assert (Colour.red original = 3);
  assert (Box.set_contents "grey" Box.{ contents = 9 } = Box.{ contents = "grey" });
  let original = Mutable.{ count = 1; label = "grey" } in
  let changed = Mutable.set_count 2 original in
  assert (original.Mutable.count = 1 && changed.Mutable.count = 2)