أنواع القيم مقابل أنواع المراجع

عائلتا الأنواع

using System;

class Program
{
    static void Main()
    {
        int valueType = 5;          // value type
        int[] referenceType = { 1, 2, 3 };  // reference type
        Console.WriteLine(valueType + ", length " + referenceType.Length);
    }
}

أنواع القيمة تحتفظ بالبيانات

using System;

class Program
{
    static void Main()
    {
        int a = 10;
        double b = 3.14;
        bool c = true;
        Console.WriteLine(a + ", " + b + ", " + c);
    }
}

الأنواع المرجعية تحتفظ بعنوان

using System;

class Box { public int Value; }

class Program
{
    static void Main()
    {
        Box b = new Box();   // b refers to a heap object
        b.Value = 42;
        Console.WriteLine(b.Value);
    }
}

دلالات النسخ: أنواع القيمة

using System;

class Program
{
    static void Main()
    {
        int a = 1;
        int b = a;   // copy
        b = 99;
        Console.WriteLine("a=" + a + ", b=" + b);
    }
}

دلالات النسخ: أنواع المرجع

using System;

class Box { public int Value; }

class Program
{
    static void Main()
    {
        Box a = new Box { Value = 1 };
        Box b = a;   // same object
        b.Value = 99;
        Console.WriteLine("a.Value=" + a.Value + ", b.Value=" + b.Value);
    }
}

البُنى أنواع قيمة

using System;

struct Point { public int X, Y; }

class Program
{
    static void Main()
    {
        Point p1 = new Point { X = 1, Y = 2 };
        Point p2 = p1;   // full copy
        p2.X = 99;
        Console.WriteLine("p1.X=" + p1.X + ", p2.X=" + p2.X);
    }
}

تمرير القيم إلى الأساليب

using System;

class Counter { public int N; }

class Program
{
    static void BumpInt(int x) { x++; }
    static void BumpObj(Counter c) { c.N++; }

    static void Main()
    {
        int i = 0;
        BumpInt(i);
        var c = new Counter();
        BumpObj(c);
        Console.WriteLine("i=" + i + ", c.N=" + c.N);
    }
}

null وأنواع المرجع

using System;

class Program
{
    static void Main()
    {
        string text = null;        // reference type can be null
        int? maybe = null;          // nullable value type
        Console.WriteLine((text == null) + ", " + (maybe == null));
    }
}

اختلافات المساواة

using System;

class Program
{
    static void Main()
    {
        int a = 5, b = 5;
        Console.WriteLine("ints: " + (a == b));   // True - same value

        object o1 = new object();
        object o2 = new object();
        Console.WriteLine("objects: " + (o1 == o2));   // False - different identity
    }
}

القيم الافتراضية

using System;

class Program
{
    static void Main()
    {
        int defaultInt = default;
        bool defaultBool = default;
        string defaultString = default;
        Console.WriteLine(defaultInt + ", " + defaultBool + ", null? " + (defaultString == null));
    }
}

جمع المفاهيم

using System;

struct Money { public decimal Amount; }
class Wallet { public decimal Amount; }

class Program
{
    static void Main()
    {
        Money m1 = new Money { Amount = 10 };
        Money m2 = m1; m2.Amount = 99;

        Wallet w1 = new Wallet { Amount = 10 };
        Wallet w2 = w1; w2.Amount = 99;

        Console.WriteLine("Money copy: " + m1.Amount + " (independent)");
        Console.WriteLine("Wallet ref: " + w1.Amount + " (shared)");
    }
}

اختبار سريع

مراجعة

using System;

struct V { public int N; }
class R { public int N; }

class Program
{
    static void Main()
    {
        V v1 = new V { N = 1 }; V v2 = v1; v2.N = 9;
        R r1 = new R { N = 1 }; R r2 = r1; r2.N = 9;
        Console.WriteLine(v1.N + " vs " + r1.N);
    }
}