F# Discriminated Unions Single case discriminated union
Example
A single case discriminated union is like any other discriminated union except that it only has one case.
// Define single-case discriminated union type.
type OrderId = OrderId of int
// Construct OrderId type.
let order = OrderId 123
// Deconstruct using pattern matching.
// Parentheses used so compiler doesn't think it is a function definition.
let (OrderId id) = order
It is useful for enforcing type safety and commonly used in F# as opposed to C# and Java where creating new types comes with more overhead.
The following two alternative type definitions result in the same single-case discriminated union being declared:
type OrderId = | OrderId of int
type OrderId =
| OrderId of int
