[C#] IEquatable<T>

搞清楚 IEquatable<T> 觀念和使用

VS 快捷鍵可以快速 override Equals 和 GetHashCode Method

手動建立的 User Class 只包含兩個 Property

public class User
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

在 class 上使用 Alt + Enter 就可以看見快捷功能，選擇 [產生 Equals 與 GetHashCode]

勾選 [IEquatable<User>] 選項

產生完整的 User Class Code

public class User : IEquatable<User>
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public override bool Equals(object obj)
    {
        return Equals(obj as User);
    }

    public bool Equals(User other)
    {
        return other != null &&
               FirstName == other.FirstName &&
               LastName == other.LastName;
    }

    public override int GetHashCode()
    {
        // VS 自動產生
        int hashCode = 1938039292;
        hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(FirstName);
        hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(LastName);
        return hashCode;
        
        // 查資料時發現，下列寫法比較常見
        return FirstName.GetHashCode() ^ LastName.GetHashCode();        
    }
}

Demo 範例

using System;

namespace IEquatableSample
{
    class Program
    {
        static void Main(string[] args)
        {
            User UserA = new User
            {
                LastName = "姓",
                FirstName = "名"
            };

            User UserB = new User
            {
                LastName = "姓",
                FirstName = "名"
            };

            Console.WriteLine($"UserA == UserB：{UserA == UserB}");
            Console.WriteLine($"UserA.Equals(UserB)：{UserA.Equals(UserB)}");
        }
    }
}

結果

• 參考資料
• 在 Visual Studio 中產生 Equals 與 GetHashCode 方法覆寫
• Object.Equals 方法
• Part 58 C# Tutorial Why should you override Equals Method
• If You Implement Iequatable T You Still Must Override Object S Equals And Gethashcode