c#用表达式树实现深拷贝功能

因为对表达式树有点兴趣，出于练手的目的，试着写了一个深拷贝的工具库。支持.net standard2.0或.net framework4.5及以上。

GitHub地址https://github.com/blurhkh/DeepCopier

nuget地址https://www.nuget.org/packages/DeepCopier

使用方法如下：

首先创建几个测试用的类型

    public class Author
    {
        public string Name { get; set; }
    }

    public class Book
    {
        public string Title { get; set; }
        public Author Author { get; set; }
        public List<string> Tags { get; set; }
    }

    public class BookDTO
    {
        public string Title { get; set; }
        public Author Author { get; set; }
        public List<string> Tags { get; set; }
    }

        Book book = new Book
        {
            Author = new Author { Name = "Author" },
            Title = "Title",
            Tags = new List<string> { "dotnet-core", "c#" }
        };

        // 用法1 深拷贝一个对象
        Book book2 = Copier.Copy(book);
        // 或一个IEnumerable<T>的实现类实例（目前仅支持一维数组和ICollection<T>的实现类）
        HashSet<Book> books = new HashSet<Book>() { book, book };
        HashSet<Book> books2 = Copier.Copy(books);

        // 用法2 新建目标类型实例，并将源对象的属性值拷贝至目标对象的对应属性
        BookDTO bookDTO = Copier.Copy<Book, BookDTO>(book);

        // 用法3 将源对象的属性值拷贝至已存在的目标对象的对应属性
        BookDTO target = new BookDTO();
        Copier.Copy(book, target);

同类的工具库比如较为常见的AutoMapper和一个Reflection.Emit操作IL写的DeepCopy（https://www.nuget.org/packages/DeepCopy/）

接下来进行一下和他们的性能对比，测试数据采用上面的Book类型，循环次数为100万次。

测试数据如下：

        Book book = new Book
        {
            Author = new Author { Name = "Author" },
            Title = "Title",
            Tags = new List<string> { "dotnet-core", "c#" }
        };

测试内容如下（本人PC的CPU为I7 4790k，不同库的测试代码分别跑在不同的程序里）：

首先和AutoMapper进行对比

BookDTO bookDTO = null;
 
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 1000000; i++)
{
    bookDTO = DeepCopier.Copier.Copy<Book, BookDTO>(book);
}
Console.WriteLine($"DeepCopier costed {sw.ElapsedMilliseconds} ms at 1st time.");
 
sw.Restart();
 
for (int i = 0; i < 1000000; i++)
{
    bookDTO = DeepCopier.Copier.Copy<Book, BookDTO>(book);
}
// 因为有了前一次的缓存，这里速度会更快
Console.WriteLine($"DeepCopier costed {sw.ElapsedMilliseconds} ms at 2nd time.");
Console.ReadLine();

            // AutoMapper需要提前配置
            AutoMapper.Mapper.Initialize(config => {
                config.CreateMap<Book, BookDTO>();
            });

            BookDTO bookDTO = null;

            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (int i = 0; i < 1000000; i++)
            {
                bookDTO = AutoMapper.Mapper.Map<Book, BookDTO>(book);
            }
            Console.WriteLine($"AutoMapper costed {sw.ElapsedMilliseconds} ms at 1st time.");

            sw.Restart();

            for (int i = 0; i < 1000000; i++)
            {
                bookDTO = AutoMapper.Mapper.Map<Book, BookDTO>(book);
            }
            Console.WriteLine($"AutoMapper costed {sw.ElapsedMilliseconds} ms at 2nd time.");
            Console.ReadLine();

            // DeepCopy只支持对自身类型的拷贝
            Book temp = null;

            Stopwatch sw = new Stopwatch();
            sw.Start();
            for (int i = 0; i < 1000000; i++)
            {
                temp = DeepCopy.DeepCopier.Copy(book);
            }
            Console.WriteLine($"DeepCopy costed {sw.ElapsedMilliseconds} ms at 1st time.");

            sw.Restart();

            for (int i = 0; i < 1000000; i++)
            {
                temp = DeepCopy.DeepCopier.Copy(book);
            }
            Console.WriteLine($"DeepCopy costed {sw.ElapsedMilliseconds} ms at 2nd time.");
            Console.ReadLine();