How to Create a True Deep Copy of a C# List?

A true deep copy method for creating List

Introduction

In many programming scenarios, it is crucial to create a truly independent copy of the original data structure. For List in C#, it is crucial to understand how to implement deep copy.

Question

Consider the following code snippet:

<code class="language-csharp">List<Book> books_1 = new List<Book>();
books_1.Add(new Book("One"));
books_1.Add(new Book("Two"));
books_1.Add(new Book("Three"));
books_1.Add(new Book("Four"));

List<Book> books_2 = new List<Book>(books_1);

books_2[0].title = "Five";
books_2[1].title = "Six";

// 对books_2的更改会反映在books_1中
textBox1.Text = books_1[0].title;
textBox2.Text = books_1[1].title;</code>

Although this code creates a new list, the Book object in books_2 is still a reference to the same object in books_1. Therefore, modifications to books_2 will affect books_1.

Solution

To create a true deep copy of List, each element of the original list must be copied. This can be achieved using the following code:

<code class="language-csharp">List<Book> books_2 = books_1.Select(book => new Book(book.title)).ToList();</code>

Each Book object in books_1 is converted into a new Book object by using LINQ's Select method. These new objects are then stored in books_2, resulting in a deep copy.

Alternatively, you can take a simpler approach using List’s ConvertAll method:

<code class="language-csharp">List<Book> books_2 = books_1.ConvertAll(book => new Book(book.title));</code>

This method returns a new list where each element is the result of transforming the corresponding element in the original list.

With this approach, books_2 and books_1 are independent of each other, and changes to one list will not affect the other.

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