การสร้างแบบจำลองโดเมนด้วยยูเนียนแยกแยะได้ (เรคคอร์ด) — จำลองใน C# 6

แนวคิด DU ใน C# 6

แท็กและเมธอดสร้าง

using System;

public enum PaymentKind { Cash, Card, Wire }

public sealed class Payment
{
  public PaymentKind Kind;

  // per-case data (only one is meaningful per instance)
  public string CardLast4; // for Card
  public string Iban;      // for Wire

  private Payment() { }

  // factories keep invariants
  public static Payment Cash()
  {
    Payment p = new Payment();
    p.Kind = PaymentKind.Cash;
    return p;
  }

  public static Payment Card(string last4)
  {
    if (string.IsNullOrEmpty(last4) || last4.Length != 4)
      throw new ArgumentException("last4 must be 4 digits", "last4");
    Payment p = new Payment();
    p.Kind = PaymentKind.Card;
    p.CardLast4 = last4;
    return p;
  }

  public static Payment Wire(string iban)
  {
    if (string.IsNullOrEmpty(iban))
      throw new ArgumentException("iban must not be empty", "iban");
    Payment p = new Payment();
    p.Kind = PaymentKind.Wire;
    p.Iban = iban;
    return p;
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Payment a = Payment.Cash();
    Payment b = Payment.Card("1234");
    Payment c = Payment.Wire("TR00BANKIBAN");
    Console.WriteLine(a.Kind + ", " + b.Kind + ", " + c.Kind);
  }
}

การจัดการรูปแบบต่าง ๆ

using System;

public enum PaymentKind { Cash, Card, Wire }

public sealed class Payment
{
  public PaymentKind Kind;
  public string CardLast4;
  public string Iban;

  public static Payment Cash()
  {
    Payment p = new Payment(); p.Kind = PaymentKind.Cash; return p;
  }
  public static Payment Card(string last4)
  {
    if (string.IsNullOrEmpty(last4) || last4.Length != 4) throw new ArgumentException("last4");
    Payment p = new Payment(); p.Kind = PaymentKind.Card; p.CardLast4 = last4; return p;
  }
  public static Payment Wire(string iban)
  {
    if (string.IsNullOrEmpty(iban)) throw new ArgumentException("iban");
    Payment p = new Payment(); p.Kind = PaymentKind.Wire; p.Iban = iban; return p;
  }
}

public static class Exhaustive
{
  public static Exception Unhandled(object x)
  {
    return new InvalidOperationException("Unhandled case: " + x);
  }
}

public class Program
{
  static string Describe(Payment p)
  {
    switch (p.Kind)
    {
      case PaymentKind.Cash: return "Cash";
      case PaymentKind.Card: return "Card ****" + p.CardLast4;
      case PaymentKind.Wire: return "Wire " + p.Iban;
      default: throw Exhaustive.Unhandled(p.Kind);
    }
  }

  public static void Main(string[] args)
  {
    Console.WriteLine(Describe(Payment.Card("9876")));
  }
}

ตัวช่วย Match แบบคล้ายผู้เยี่ยมชม

using System;

public enum PaymentKind { Cash, Card, Wire }

public sealed class Payment
{
  public PaymentKind Kind;
  public string CardLast4;
  public string Iban;

  public static Payment Cash() { Payment p = new Payment(); p.Kind = PaymentKind.Cash; return p; }
  public static Payment Card(string last4) { Payment p = new Payment(); p.Kind = PaymentKind.Card; p.CardLast4 = last4; return p; }
  public static Payment Wire(string iban) { Payment p = new Payment(); p.Kind = PaymentKind.Wire; p.Iban = iban; return p; }
}

public static class PaymentMatch
{
  public static T Match<T>(
    Payment p,
    Func<T> onCash,
    Func<string, T> onCard,
    Func<string, T> onWire)
  {
    switch (p.Kind)
    {
      case PaymentKind.Cash: return onCash();
      case PaymentKind.Card: return onCard(p.CardLast4);
      case PaymentKind.Wire: return onWire(p.Iban);
      default: throw new InvalidOperationException("Unhandled: " + p.Kind);
    }
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Payment p = Payment.Card("1234");
    string summary = PaymentMatch.Match(
      p,
      delegate { return "Cash"; },
      delegate(string last4) { return "Card ****" + last4; },
      delegate(string iban) { return "Wire " + iban; }
    );
    Console.WriteLine(summary);
  }
}

ใช้เมธอดสร้างบังคับเงื่อนไขคงรูป

using System;

public enum ResultKind { Ok, Error }

public sealed class Result
{
  public ResultKind Kind;
  public string Message; // only for Error
  public int Value;      // only for Ok

  private Result() { }

  public static Result Ok(int value)
  {
    Result r = new Result();
    r.Kind = ResultKind.Ok;
    r.Value = value;
    r.Message = null;
    return r;
  }

  public static Result Error(string message)
  {
    if (string.IsNullOrEmpty(message)) throw new ArgumentException("message");
    Result r = new Result();
    r.Kind = ResultKind.Error;
    r.Message = message;
    r.Value = 0;
    return r;
  }
}

public class Program
{
  static string Show(Result r)
  {
    switch (r.Kind)
    {
      case ResultKind.Ok: return "OK: " + r.Value;
      case ResultKind.Error: return "ERROR: " + r.Message;
      default: throw new InvalidOperationException("Unhandled: " + r.Kind);
    }
  }

  public static void Main(string[] args)
  {
    Console.WriteLine(Show(Result.Ok(5)));
    Console.WriteLine(Show(Result.Error("Boom")));
  }
}

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