التصميم الساكن مقابل تصميم النسخ

قرار تصميمي

using System;

class Program
{
    // Depends only on inputs -> good static method
    static int Max(int a, int b) => a > b ? a : b;

    static void Main()
    {
        Console.WriteLine(Max(3, 8));
    }
}

استخدم static للمنطق عديم الحالة

using System;

static class Convert2
{
    public static double MilesToKm(double miles) => miles * 1.60934;
}

class Program
{
    static void Main()
    {
        Console.WriteLine(Convert2.MilesToKm(10).ToString("0.0") + " km");
    }
}

استخدم instance للحالة

using System;

class Counter
{
    private int _count;
    public void Increment() => _count++;
    public int Value => _count;
}

class Program
{
    static void Main()
    {
        var a = new Counter();
        var b = new Counter();
        a.Increment();
        a.Increment();
        b.Increment();
        Console.WriteLine("a=" + a.Value + ", b=" + b.Value);
    }
}

الحالة المشتركة هي حالة عامة

using System;

class BadCart
{
    public static int Items;   // shared by EVERYONE -> usually wrong for a cart
}

class Program
{
    static void Main()
    {
        BadCart.Items++;
        BadCart.Items++;
        Console.WriteLine("All carts share: " + BadCart.Items);
    }
}

قابلية الاختبار

using System;

static class Calc
{
    public static int Add(int a, int b) => a + b;   // trivially testable
}

class Program
{
    static void Main()
    {
        Console.WriteLine(Calc.Add(2, 2) == 4 ? "pass" : "fail");
    }
}

استخدم static للمساعدات المنشئة

using System;

class Color
{
    public int R, G, B;
    private Color(int r, int g, int b) { R = r; G = g; B = b; }

    public static Color Red() => new Color(255, 0, 0);
    public static Color White() => new Color(255, 255, 255);
}

class Program
{
    static void Main()
    {
        var c = Color.Red();
        Console.WriteLine(c.R + "," + c.G + "," + c.B);
    }
}

لا تستخدم static لمجرد تجنب new

using System;

class Player
{
    public string Name;
    public int Health = 100;
    public void TakeDamage(int d) => Health -= d;
}

class Program
{
    static void Main()
    {
        var p1 = new Player { Name = "A" };
        var p2 = new Player { Name = "B" };
        p1.TakeDamage(30);
        Console.WriteLine(p1.Name + ": " + p1.Health + ", " + p2.Name + ": " + p2.Health);
    }
}

الملاءمة بين الاثنين

using System;

class Invoice
{
    private static int _seq = 1000;
    public readonly int Number;
    public decimal Amount;

    public Invoice(decimal amount)
    {
        Number = _seq++;
        Amount = amount;
    }
}

class Program
{
    static void Main()
    {
        var i1 = new Invoice(50m);
        var i2 = new Invoice(75m);
        Console.WriteLine(i1.Number + " / " + i2.Number);
    }
}

مشكلة التزامن

using System;

class SafeCalc
{
    // No shared mutable state -> naturally thread-safe
    public static long Factorial(int n)
    {
        long result = 1;
        for (int i = 2; i <= n; i++) result *= i;
        return result;
    }
}

class Program
{
    static void Main()
    {
        Console.WriteLine(SafeCalc.Factorial(5));
    }
}

قاعدة عامة بسيطة

using System;

class Temperature
{
    public double Celsius;                                  // instance state
    public static double ToF(double c) => c * 9 / 5 + 32;   // stateless helper
}

class Program
{
    static void Main()
    {
        var t = new Temperature { Celsius = 30 };
        Console.WriteLine(Temperature.ToF(t.Celsius));
    }
}

تجميع المفاهيم

using System;

static class TaxRules
{
    public static decimal Apply(decimal amount, decimal rate) => amount + amount * rate;
}

class Sale
{
    public decimal Subtotal;
    public decimal Total(decimal rate) => TaxRules.Apply(Subtotal, rate);
}

class Program
{
    static void Main()
    {
        var s = new Sale { Subtotal = 100m };
        Console.WriteLine(s.Total(0.2m));
    }
}

اختبار سريع

مراجعة

using System;

static class Util { public static int Sq(int n) => n * n; }

class Box { public int Size; public int Area() => Util.Sq(Size); }

class Program
{
    static void Main()
    {
        var box = new Box { Size = 4 };
        Console.WriteLine(box.Area());
    }
}