下面演示如何创建一个不可变的轻型类，该类仅用于封装一组自动实现的属性。 当你必须使用引用类型语义时，请使用此种构造而不是结构。

可通过以下方法来实现不可变的属性：

• 仅声明 get 访问器，使属性除了能在该类型的构造函数中可变，在其他任何位置都不可变。
• 声明 init 访问器而不是 set 访问器，这使属性只能在构造函数中进行设置，或者通过使用对象初始值设定项设置。
• 将 set 访问器声明为专用。 属性可在该类型中设置，但它对于使用者是不可变的。

可以将 required 修饰符添加到属性声明中，以强制调用方将属性设置为初始化新对象的一部分。

下面的示例显示了只有 get 访问器的属性与具有 get 和 private set 的属性的区别。

class Contact
{
    public string Name { get; }
    public string Address { get; private set; }

    public Contact(string contactName, string contactAddress)
    {
        // Both properties are accessible in the constructor.
        Name = contactName;
        Address = contactAddress;
    }

    // Name isn't assignable here. This will generate a compile error.
    //public void ChangeName(string newName) => Name = newName;

    // Address is assignable here.
    public void ChangeAddress(string newAddress) => Address = newAddress;
}

示例

以下示例演示了实现具有自动实现属性的不可变类的两种方法。 这两种方法均使用 private set 声明其中一个属性，使用单独的 get 声明另一个属性。 第一个类仅使用构造函数来初始化属性，第二个类则使用可调用构造函数的静态工厂方法。

// This class is immutable. After an object is created,
// it cannot be modified from outside the class. It uses a
// constructor to initialize its properties.
class Contact
{
    // Read-only property.
    public string Name { get; }

    // Read-write property with a private set accessor.
    public string Address { get; private set; }

    // Public constructor.
    public Contact(string contactName, string contactAddress)
    {
        Name = contactName;
        Address = contactAddress;
    }
}

// This class is immutable. After an object is created,
// it cannot be modified from outside the class. It uses a
// static method and private constructor to initialize its properties.
public class Contact2
{
    // Read-write property with a private set accessor.
    public string Name { get; private set; }

    // Read-only property.
    public string Address { get; }

    // Private constructor.
    private Contact2(string contactName, string contactAddress)
    {
        Name = contactName;
        Address = contactAddress;
    }

    // Public factory method.
    public static Contact2 CreateContact(string name, string address)
    {
        return new Contact2(name, address);
    }
}

public class Program
{
    static void Main()
    {
        // Some simple data sources.
        string[] names = ["Terry Adams","Fadi Fakhouri", "Hanying Feng",
                            "Cesar Garcia", "Debra Garcia"];
        string[] addresses = ["123 Main St.", "345 Cypress Ave.", "678 1st Ave",
                                "12 108th St.", "89 E. 42nd St."];

        // Simple query to demonstrate object creation in select clause.
        // Create Contact objects by using a constructor.
        var query1 = from i in Enumerable.Range(0, 5)
                    select new Contact(names[i], addresses[i]);

        // List elements cannot be modified by client code.
        var list = query1.ToList();
        foreach (var contact in list)
        {
            Console.WriteLine("{0}, {1}", contact.Name, contact.Address);
        }

        // Create Contact2 objects by using a static factory method.
        var query2 = from i in Enumerable.Range(0, 5)
                        select Contact2.CreateContact(names[i], addresses[i]);

        // Console output is identical to query1.
        var list2 = query2.ToList();

        // List elements cannot be modified by client code.
        // CS0272:
        // list2[0].Name = "Eugene Zabokritski";
    }
}

/* Output:
    Terry Adams, 123 Main St.
    Fadi Fakhouri, 345 Cypress Ave.
    Hanying Feng, 678 1st Ave
    Cesar Garcia, 12 108th St.
    Debra Garcia, 89 E. 42nd St.
*/