C#杂记

电玩女神 2022-05-26 09:40 186阅读 0赞

# out使用陷阱 #

using System;
    using System.Collections.Generic;
    
    namespace BasicTest
    {
        class Program
        {
            static void Main(string[] args)
            {
                Dictionary<string, string> fruits = new Dictionary<string, string> { { "a", "apple" }, { "b", "banana" }, { "c", "cherry" } };
    
                foreach (var item in fruits)
                {
                    Console.WriteLine("fruits Before：");
                    Console.WriteLine($"key：{item.Key}，value：{item.Value}");
                    Console.WriteLine("\n");
                }
    
                fruits.TryGetValue("b", out var fruitName);
                fruitName = "blueberry";  // 等效于fruitName = new string("blueberry".ToCharArray()); 不等效于fruits["b"] = "blueberry"
                //fruits["b"] = "blueberry"; //这个与上面一行有本质区别
    
                foreach (var item in fruits)
                {
                    Console.WriteLine("fruits After：");
                    Console.WriteLine($"key：{item.Key}，value：{item.Value}");
                    Console.WriteLine("\n");
                }
    
    
                Dictionary<string, Dictionary<string, long>> projectsVersoins = new Dictionary<string, Dictionary<string, long>>();
    
                Dictionary<string, long> fooVersion = new Dictionary<string, long>
                {
                    { "test",123 },
                    { "qa",456},
                    { "uat",789},
                    { "stage",147},
                    { "product",258}
                };
    
                Dictionary<string, long> barVersion = new Dictionary<string, long>
                {
                    { "test",369 },
                    { "qa",159},
                    { "uat",357},
                    { "stage",951},
                    { "product",753}
                };
    
                projectsVersoins.Add("naruto", fooVersion);
                projectsVersoins.Add("sasuke", barVersion);
    
                Dictionary<string, long> projectVersions = new Dictionary<string, long>
                {
                    { "test",999 },   // 999 > 123
                    { "qa",456},
                    { "uat",789},
                    { "stage",147},
                    { "product",258}
                };
    
    
                foreach (var item in projectsVersoins["naruto"])
                {
                    Console.WriteLine("ProjectVersion Before：");
                    Console.WriteLine($"key：{item.Key}，value：{item.Value}");
                    Console.WriteLine("\n");
                }
    
                if (!projectsVersoins.TryGetValue("naruto", out var oriProjectVersions))
                {
                    Console.WriteLine("本测试代码不应该跑到这里，否则请查看代码");
                }
                oriProjectVersions["test"] = 999;  //这个等效于projectsVersoins["naruto"]["test"] = newVer.Value;
                //fruitName.[0] = 'c';
                //fruitName = "clueberry";
    
                //oriProjectVersions = new Dictionary<string, long>();
                //fruitName = new string("blueberry".ToCharArray());
    
    
    
                //foreach (var newVer in projectVersions)
                //{ 
                // if (!oriProjectVersions.TryGetValue(newVer.Key, out var ver) || newVer.Value > ver)
                // { 
                // oriProjectVersions[newVer.Key] = newVer.Value;
                // //projectsVersoins["naruto"][newVer.Key] = newVer.Value;
                // }
                //}
    
                foreach (var item in projectsVersoins["naruto"])
                {
                    Console.WriteLine("ProjectVersion After：");
                    Console.WriteLine($"key：{item.Key}，value：{item.Value}");
                    Console.WriteLine("\n");
                }
    
    
                Console.ReadLine();
            }
        }
    }

###### 输出： ######

fruits Before：  
key：a，value：apple

fruits Before：  
***key：b，value：banana***

fruits Before：  
key：c，value：cherry

fruits After：  
key：a，value：apple

fruits After：  
***key：b，value：banana***

fruits After：  
key：c，value：cherry

ProjectVersion Before：  
***key：test，value：123***

ProjectVersion Before：  
key：qa，value：456

ProjectVersion Before：  
key：uat，value：789

ProjectVersion Before：  
key：stage，value：147

ProjectVersion Before：  
key：product，value：258