NewType in F#

newtype.fs

// current type abbreviations in F#
type A = Guid
type B = Guid

let foo (x : A) = x.ToString()
let b = B.NewGuid()
foo(b) // type checks

// proposed newtype abbreviations
newtype A = Guid
newtype B = Guid

let foo (x : A) = x.ToString()
let b = B.NewGuid()
foo(b) // type error

// newtype abbreviations should generate explicit conversion methods
let g : Guid = B.ToGuid b
let b : B = B.FromGuid g

// alternative attribute-based approach
[<NewType>]
type A = Guid
[<NewType>]
type B = Guid

In other words, the struct approach is probably the better way of solving this.