Příklad k článku http://rarous.net/weblog/451-jak-teda-s-tema-vyjimkama-v-busines-logice.aspx

PatternMatching.cs

using System;

class Program
{
    static void Main()
    {
        var result1 = Authenticate("me", "password");
        PrintAuthResult(result1);

        var result2 = Authenticate("ja", "heslo");
        PrintAuthResult(result2);
    }

    static AuthenticationResult Authenticate(string login, string password)
    {
        if (password == "heslo")
            return new Authenticated(new User(login));
        else
            return new NotAuthenticated();
    }

    static void PrintAuthResult(AuthenticationResult result)
    {
        result.Match(
            some: user => Console.WriteLine("yes: {0}", user.Login),
            none: () => Console.WriteLine("no")
        );
    }
}

public class User
{
    public User(string login)
    {
        Login = login;
    }

    public string Login { get; private set; }
}

public interface AuthenticationResult { }

public class NotAuthenticated : AuthenticationResult { }

public class Authenticated : AuthenticationResult
{
    public Authenticated(User user)
    {
        User = user;
    }

    public User User { get; private set; }
}

public static class AuthenticationResultExtension
{
    public static void Match(this AuthenticationResult result, Action<User> some, Action none)
    {
        var authenticated = result as Authenticated;
        if (authenticated == null)
            none();
        else
            some(authenticated.User);
    }
}

PatternMatching.fs

type User(login: string) = class
    member x.Login = login
end

type AuthenticationResult =
    | NotAuthenticated
    | Authenticated of User
  
let Authenticate (login: string) (password: string) =
    if password = "heslo" then  Authenticated(new User(login))
    else NotAuthenticated

let PrintAuthResult (result: AuthenticationResult) =
    match result with
    | AuthenticationResult.Authenticated(result) -> printfn "yes: %s" result.Login
    | AuthenticationResult.NotAuthenticated -> printfn "no"

let main() =
    let result1 = Authenticate "me" "password"
    PrintAuthResult result1
    let result2 = Authenticate "ja" "heslo"
    PrintAuthResult result2

main()