Example
F# uses the type keyword to create different kind of types.
- Type aliases
- Discriminated union types
- Record types
- Interface types
- Class types
- Struct types
Examples with equivalent C# code where possible:
// Equivalent C#:
// using IntAliasType = System.Int32;
type IntAliasType = int // As in C# this doesn't create a new type, merely an alias
type DiscriminatedUnionType =
| FirstCase
| SecondCase of int*string
member x.SomeProperty = // We can add members to DU:s
match x with
| FirstCase -> 0
| SecondCase (i, _) -> i
type RecordType =
{
Id : int
Name : string
}
static member New id name : RecordType = // We can add members to records
{ Id = id; Name = name } // { ... } syntax used to create records
// Equivalent C#:
// interface InterfaceType
// {
// int Id { get; }
// string Name { get; }
// int Increment (int i);
// }
type InterfaceType =
interface // In order to create an interface type, can also use [<Interface>] attribute
abstract member Id : int
abstract member Name : string
abstract member Increment : int -> int
end
// Equivalent C#:
// class ClassType : InterfaceType
// {
// static int increment (int i)
// {
// return i + 1;
// }
//
// public ClassType (int id, string name)
// {
// Id = id ;
// Name = name ;
// }
//
// public int Id { get; private set; }
// public string Name { get; private set; }
// public int Increment (int i)
// {
// return increment (i);
// }
// }
type ClassType (id : int, name : string) = // a class type requires a primary constructor
let increment i = i + 1 // Private helper functions
interface InterfaceType with // Implements InterfaceType
member x.Id = id
member x.Name = name
member x.Increment i = increment i
// Equivalent C#:
// class SubClassType : ClassType
// {
// public SubClassType (int id, string name) : base(id, name)
// {
// }
// }
type SubClassType (id : int, name : string) =
inherit ClassType (id, name) // Inherits ClassType
// Equivalent C#:
// struct StructType
// {
// public StructType (int id)
// {
// Id = id;
// }
//
// public int Id { get; private set; }
// }
type StructType (id : int) =
struct // In order create a struct type, can also use [<Struct>] attribute
member x.Id = id
end
