Base C #: C # in deep and shallow copy copy

First, what is the deep and shallow copy copy

For all object-oriented languages, a copy will always be prone to lead to the topics discussed, C # is no exception. Such questions asked in the interview is extremely easy, we should understand the deep and shallow copy copy basic concepts on the basis of further consideration of how to support the copy of the object from a design point of view.

In System.Object class, a protected method object.MemberwiseClone (), this method implements the replication object. In fact, it has achieved what we call a shallow copy.

The so-called shallow copy means a copy of an object when a copy of all references to the non-static member value types and reference types all members of the original object. In other words, the new object and the original object will be shared by all members of the actual object reference type. The relative, a deep copy refers not only to copy all of the non-static member value type, but also copy all the actual object reference type member. The concept of deep copy and shallow copy is recursive, that is when a member of reference type contains a reference type when another member, when the copy will implement the same strategy of copying its internal members.

Shallow copy mode is shown below:

Deep copy schematic shown below:

Type the base class for all types System.Object already have achieved a shallow copy, type have to do is open a copy of the interface, and the usual, this interface will be implemented by means of realization ICloneable interface. ICLoneable contains a Clone method only. The method may be implemented either as a shallow copy may be implemented as a deep copy, how to choose the specific needs of the type according to the specific needs. The following code provides a simple example of a deep copy of:

using System;

namespace DeepCopy
{
    class Program
    {
        static void Main(string[] args)
        {
            // 定义原始对象
            DpCopy dc = new DpCopy();
            dc._i = 10;
            dc._a = new A();

            // 定义深拷贝对象
            DpCopy deepClone = (DpCopy)dc.Clone();
            // 定义浅拷贝对象
            DpCopy shadowclone = (DpCopy)dc.MemberwiseClone();
            // 深拷贝的复制对象将拥有自己的引用类型成员对象
            // 所以这里的赋值不会影响原始对象
            deepClone._a._s = "我是深拷贝的A";
            Console.WriteLine(dc);
            Console.WriteLine(deepClone);
            Console.WriteLine("\r\n");

            // 浅拷贝的复制对象共享原始对象的引用类型成员对象
            // 所以这里的赋值将影响原始对象
            shadowclone._a._s = "我是浅拷贝的A";
            Console.WriteLine(dc);
            Console.WriteLine(shadowclone);

            Console.ReadKey();
        }
    }

    public class DpCopy : ICloneable
    {
        public int _i = 0;
        public A _a = new A();
        public object Clone()
        {
            // 实现深拷贝
            DpCopy newDc = new DpCopy();
            // 重新实例化一个引用类型变量
            newDc._a = new A();
            // 给新引用类型变量的成员值
            newDc._a._s = _a._s;
            newDc._i = _i;
            return newDc;
        }

        // 实现浅拷贝
        public new object MemberwiseClone()
        {
            return base.MemberwiseClone();
        }

        /// <summary>
        /// 重写类的ToString()方法
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return "I的值为：" + _i.ToString() + ",A为：" + _a._s;
        }
    }

    /// <summary>
    /// 包含一个引用成员的类型
    /// </summary>
    public class A
    {
        public string _s = "我是原始A";
    }
}

在上面的代码中，类型DpCopy通过ICLoneable接口的Clone方法提供了深拷贝，并且通过提供一个MemberwiseClone的公共方法提供了浅拷贝。DpCopy类型具有一个值类型成员和一个引用类型成员，引用类型成员在浅拷贝和深拷贝时将展现不同的特性，浅拷贝的原始对象和目标对象公用了一个引用类型成员对象，这在程序的执行结果中可以清楚地看到：

有的参考资料上说C#中的深拷贝通过ICloneable接口来实现。这句话并不正确。事实上任何名字的方法都可以用来实现深拷贝，并且没有任何语法来规定深拷贝只能通过Clone方法来实现。Clone这个名字只是一种习惯的称呼，而实现ICloneable只能带来一般接口的通用便利性，而并没有任何关于拷贝的特殊性。

一般可被继承的类型应该避免实现ICloneable接口，因为这样做将强制所有的子类型都需要实现ICloneable接口，否则将使类型的深拷贝不能覆盖子类的新成员。

二、总结

浅拷贝是指复制类型中的所有值类型成员，而只赋值引用类型成员的引用，并且使目标对象共享原对象的引用类型成员对象。深拷贝是指同时复制值类型成员和引用类型成员的对象。浅拷贝和深拷贝的概念都是递归的。System.Object中的MemberwiseClone已经实现了浅拷贝，但它是一个受保护的方法。无论深拷贝还是浅拷贝，都可以通过实现ICloneable接口的Clone方法来实现，可被继承的类型需要谨慎地实现ICloneable接口，因为这将导致所有的子类型都必须实现ICloneable接口。