F# Discriminated Union usage from C# [duplicate]

Answer 1

Assuming that we need to calculate the area of each Shape polymorphically.

In C# we would normally create a hypothetical object hierarchy and a Visitor. In this example, we would have to create a ShapeVisitor class and then a derived ShapeAreaCalculator visitor class.

In F#, we can use Pattern Matching on the Shape type:

let rectangle = Rectangle(1.3, 10.0)
let circle = Circle (1.0)

let calculateArea shape =
    match shape with
    | Circle radius -> 3.141592654 * radius * radius
    | Rectangle (height, width) -> height * width

let rectangleArea = calculateArea(rectangle)
// -> 1.3 * 10.0

let circleArea = calculateArea(circle)
// -> 3.141592654 * 1.0 * 1.0