用表達式樹實現深拷貝功能

因為對錶達式樹有點興趣，出於練手的目的，試著寫了一個深拷貝的工具庫。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：

首先創建幾個測試用的類型

    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 深拷貝一個對象
        Book book2 = Copier.Copy(book);
        // 或一個IEnumerable<T>的實現類實例（目前僅支持一維數組和ICollection<T>的實現類）
        HashSet<Book> books = new HashSet<Book>() { book, book };
        HashSet<Book> books2 = Copier.Copy(books);

        // 用法2 新建目標類型實例，並將源對象的屬性值拷貝至目標對象的對應屬性
        BookDTO bookDTO = Copier.Copy<Book, BookDTO>(book);

        // 用法3 將源對象的屬性值拷貝至已存在的目標對象的對應屬性
        BookDTO target = new BookDTO();
        Copier.Copy(book, target);

同類的工具庫比如較為常見的AutoMapper和一個Reflection.Emit操作IL寫的DeepCopy（https://www.nuget.org/packages/DeepCopy/）

接下來進行一下和他們的性能對比，測試數據採用上面的Book類型，迴圈次數為100萬次。

測試數據如下：

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

測試內容如下（本人PC的CPU為I7 4790k，不同庫的測試代碼分別跑在不同的程式里）：

首先和AutoMapper進行對比

            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);
            }
            // 因為有了前一次的緩存，這裡速度會更快
            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只支持對自身類型的拷貝
            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();