{C#}设计模式辨析.单例

背景

• 调用唯一公共资源时，重复生成实例既不经济也无必要

示例

using System;
using static System.Console;

namespace DesignPattern_Singleton
{
    public class Singleton
    {
        // 私有构造器，禁止类外实例化
        private Singleton() { }

        // 共用实例必须静态
        public static Singleton Instance = Lazy.Value;

        // 懒对象：延迟到首次调用时生成，且多线程安全
        private static Lazy<Singleton> Lazy
            => new Lazy<Singleton>(() => new Singleton());

        public void Print()
            => WriteLine("The printer is printing...");
    }

    class Demo
    {
        static void Main(string[] args)
        {
            var printer1 = Singleton.Instance;
            var printer2 = Singleton.Instance;
            WriteLine($"The printers are {(printer1 == printer2 ? "same" : "different")}.");

            printer1.Print();

            ReadKey();
        }
    }
}