dotnet
Private constructor requires attribute
When generating a signature file the result is somewhat unexpected.
Repro steps
module Telplin
type A private () =
member a.Foo () = ()
leads to
module Telplin
type A =
member Foo: unit -> unit
Expected behaviour
This should have [<Class>] attribute.
Actual behaviour
Missing attribute does not compile.
Related information
FCS: FSharpCheckFileResults.GenerateSignature
@nojaf Are you sure it's specifically about private constructors? I can reproduce it without adding the type to implementation file, so neither constructor nor its visibility change anything. I think the compiler wants to say that it can't decide which representation to use, based on the single property member in the signature file.
Expected behaviour
This should have
[<Class>]attribute.
I think the rules are a bit more complicated than this. Consider this, for example:
[<Struct>]
type A private (i: int) =
member a.Foo = 1
The compiler suggests to use Class, Struct, or Sealed, so we need to choose the attribute accordingly.
Adding private new: unit -> A to the signature removes the need to add the attribute.
Whether the attribute should be Class does indeed depend on what the actual type is.
However, I do believe structs are generated correctly.
Btw, what is generated for private type representations?
type U1 =
private
| A of int
member this.P = 1
type U2 =
private
| A of int
Something like this?
[<Sealed>]
type U1 =
member P: int
type U2
Btw, what is generated for private type representations?
Run the compiler with --allsigs flag and you will know 😉.