Hi Tim,

The `x.[i] <- v` syntax maps to `String.set` function, that has type `string -> char -> unit`, the array subscription syntax uses parentheses instead of the brackets. So in your case, it should be

x.array_field.(1) <- 3

If you are concerned with the warning, that is emitted before the error. Then this is expected, as `x.[i] <- v` is a syntactic sugar to the `String.set` and it is translated on the lexing level. Thus the type checker never sees the array/string/bigarray subscript operators (as they are not present in the AST)

Regards,

Ivan

On Tue, May 16, 2017 at 12:58 PM, Tim Leonard <Tim@timleonard.us> wrote:

Is type inference working as expected here, or is this a bug?

# type record_type = { array_field : int array };;
type record_type = { array_field : int array; }
# let test_function_1 x = Array.set x.array_field 1 3;;
val test_function_1 : record_type -> unit = <fun>
# let test_function_2 x = x.array_field.[1] <- 3;;
Characters 24-46:
let test_function_2 x = x.array_field.[1] <- 3;;
^^^^^^^^^^^^^^^^^^^^^^
Warning 3: deprecated: String.set
Use Bytes.set instead.
Characters 24-37:
let test_function_2 x = x.array_field.[1] <- 3;;
^^^^^^^^^^^^^
Error: This expression has type int array
but an expression was expected of type bytes = string
#