F# Casting and Conversions

Conversion is a process of converting type of a value to the other required type. It can be primitive or object type.

F# allows casting and conversion of primitive types and object types.

F# Conversion Example

let x : int = 44                     // integer value
let y : byte = byte x          // conversion integer to byte

printfn "y = %d" y                // byte value

let z : int = int y                // conversion byte into integer
printf "z = %d" z             // integer value

Output:

y = 44
z = 44

F# Type Casting (Upcasting, and Downcasting) Example

F# allows us to cast object of one type to another type by using :> operator. This operator is used to upcast object. we can downcast object by using :?> operator. We have used these operators in the following program. Let's see an example.

type BaseClass() =
 class
  member this.ShowClassName()=
    printfn "BaseClass"
 end

type DerivedClass() = 
 class
  inherit BaseClass()
  member this.ShowClassName()=
   printfn "DerivedClass"
 end

let baseClass = new BaseClass()            
let derivedClass : DerivedClass = new DerivedClass()
baseClass.ShowClassName()    
derivedClass.ShowClassName()
let castIntoBaseClass = derivedClass :> BaseClass        // upcasting 
castIntoBaseClass.ShowClassName()
let castIntoDerivedClass = baseClass :?> DerivedClass   // downcasting
castIntoDerivedClass.ShowClassName()

Output: