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Subtyping and constructors
f#compiler
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type I1 =
  abstract DoSomething : unit -> unit

let f (x : #I1) =
  let x = x :> I1
  x.DoSomething()

type T(x : #I1) =
  let x = x :> I1

In the example above, compiler does not complain about 'f' definition.
However, T(...) produces the following warning:

warning FS0064: This construct causes code to be less generic than indicated by its type annotations. The type variable implied by the use of a '#', '_' or other type annotation at or near '...' has been constrained to be type 'I1'.

Is it a bug, or I'm missing something?

.

I think that it's expected behavior. A flexible type annotation implicitly defines a type variable; however type definitions must explicitly declare all type variables that they use. For the same reason, this won't work:

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type T(x:'a) =

  ...
By on 1/16/2011 12:33 PM ()

Ahhhaaa... Moving the flexible type parameter and the up-cast to the static factory method, of cause, works perfectly.

Although "common sense" tells me that it is the constructor that is generic, not the type itself.

By on 1/16/2011 1:16 PM ()

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