讀書筆記：CLR var C# 第12章
阿新 • • 發佈：2018-04-01
clr data ase com esp ring 不能 program lcs
1 using System; 2 using System.Collections.Generic; 3 using System.IO; 4 using System.Linq; 5 using System.Text; 6 7 namespace ClrVarCSharp.C12Generic 8 { 9 class Program 10 { 11 public static void Main(string[] args) 12 { 13 //A.Test1(); 14 //B.Test2(); 15 //C.Test2(); 16 //Test3(); 17 //Test4(); 18 //Test5(); 19 20 } 21 22 //12.2.1 開放類型和封閉類型 23 public sealed class DictionaryStringKey<TValue> : Dictionary<string, TValue> { } 24 public static classA 25 { 26 public static void Test1() 27 { 28 object o = null; 29 30 Type t = typeof(Dictionary<,>); 31 o = CreateInstance(t); //創建開放類型實例失敗 32 Console.WriteLine(); 33 34 t = typeof(DictionaryStringKey<>); //開放類型 35 o = CreateInstance(t); 36 Console.WriteLine(); 37 38 t = typeof(DictionaryStringKey<Guid>); 39 o = CreateInstance(t); 40 Console.WriteLine(o.GetType()); 41 42 } 43 44 private static object CreateInstance(Type t) 45 { 46 object o = null; 47 try 48 { 49 o = Activator.CreateInstance(t); 50 Console.WriteLine("已創建 {0} 的實例。", t.ToString()); 51 } 52 catch (ArgumentException e) 53 { 54 Console.WriteLine(e.Message); 55 } 56 return o; 57 } 58 } 59 60 //12.2.2 泛型類型和繼承 61 //該鏈表只能接受一種類型 62 class B 63 { 64 sealed class Node<T> 65 { 66 public T m_data; 67 public Node<T> m_next; 68 public Node(T data) : this(data, null) 69 { 70 71 } 72 public Node(T data, Node<T> next) 73 { 74 m_data = data; 75 m_next = next; 76 } 77 public override string ToString() 78 { 79 return m_data.ToString() + 80 ((m_next != null) ? m_next.ToString() : string.Empty); 81 } 82 } 83 public static void Test2() 84 { 85 Node<char> head = new Node<char>(‘C‘); 86 head = new Node<char>(‘B‘, head); 87 head = new Node<char>(‘A‘, head); 88 Console.WriteLine(head.ToString()); 89 } 90 } 91 //該鏈表可接受不同的類型 92 class C 93 { 94 class Node 95 { 96 protected Node m_next; 97 public Node(Node next) 98 { 99 m_next = next; 100 } 101 } 102 sealed class TypeNode<T> : Node 103 { 104 public T m_data; 105 public TypeNode(T data) : this(data, null) 106 { 107 108 } 109 public TypeNode(T data, Node next) : base(next) 110 { 111 m_data = data; 112 } 113 public override string ToString() 114 { 115 return m_data.ToString() + 116 ((m_next != null) ? m_next.ToString() : string.Empty); 117 } 118 } 119 public static void Test2() 120 { 121 Node head = new TypeNode<char>(‘.‘); 122 head = new TypeNode<DateTime>(DateTime.Now, head); 123 head = new TypeNode<string>("Today is ", head); 124 Console.WriteLine(head.ToString()); 125 } 126 } 127 128 //12.2.3 泛型類型同一性 129 List<DateTime> dt1 = new List<DateTime>(); 130 internal sealed class DateTimeList : List<DateTime> { /* 內部無需任何代碼 */ } //DateTimeList與DateTime是兩個不同的類型 131 //using DateTimeList = System.Collections.Generic.List<System.DateTime>; //簡化代碼又保證是同一類型 132 static void Test3() 133 { 134 DateTimeList dt2 = new DateTimeList(); //通過以上定義，簡化了<> 135 bool sameType = (typeof(List<DateTime>) == typeof(DateTimeList)); 136 Console.WriteLine(sameType); 137 } 138 139 //12.6 泛型方法 140 sealed class GenericType<T> 141 { 142 private T m_value; 143 public GenericType(T value) { m_value = value; } 144 public TOutput Converter<TOutput>() 145 { 146 TOutput result = (TOutput)Convert.ChangeType(m_value, typeof(TOutput)); 147 return result; 148 } 149 } 150 151 private static void Swap<T>(ref T o1, ref T o2) 152 { 153 T temp = o1; 154 o1 = o2; 155 o2 = temp; 156 } 157 158 //12.8 可驗證性和約束 159 public static T Min<T>(T o1, T o2) where T : IComparable<T> 160 { 161 if (o1.CompareTo(o2) < 0) 162 return o1; 163 return o2; 164 } 165 166 static void Test4() 167 { 168 object o1 = "X2009"; 169 object o2 = "abc"; 170 //object oMin = Min<object>(o1, o2); //編譯錯誤 171 } 172 173 //泛型類型/方法重載 174 //只能定義基於參數數量的重載 175 sealed class AType { } 176 sealed class AType<T> { } 177 sealed class AType<T1, T2> { } 178 //不能定義僅基於約束的重載 179 //sealed class AType<T> where T : IComparable<T> { } 180 //不能定義基於名稱的重載 181 //sealed class AType<T3, T4> { } 182 183 //12.8.1 主要約束，約束為非密封類的一個引用類型 184 sealed class PrimaryConstraintOfStream<T> where T : Stream 185 { 186 public void M(T stream) 187 { 188 stream.Close(); 189 } 190 } 191 //12.8.2 次要約束，約束為接口類型 192 193 //用一個泛型來約束另一個泛型：指定參數是約束類型或其派生類型 194 static List<T2> ConvertIList<T1, T2>(IList<T1> list) where T1 : T2 195 { 196 List<T2> baseList = new List<T2>(list.Count); 197 for (int index = 0; index < list.Count; index++) 198 { 199 baseList.Add(list[index]); 200 } 201 return baseList; 202 } 203 204 static void Test5() 205 { 206 IList<string> ls = new List<string>(); 207 ls.Add("A String"); 208 209 //IList<string>轉換為IList<object> 210 IList<object> lo = ConvertIList<string, object>(ls); 211 212 IList<IComparable> lc = ConvertIList<string, IComparable>(ls); 213 214 IList<IComparable<string>> lcs = ConvertIList<string, IComparable<string>>(ls); 215 216 IList<string> ls2 = ConvertIList<string, string>(ls); 217 218 //IList<Exception> le = ConvertIList<string, Exception>(ls); 219 } 220 221 //12.8.3 構造器約束 222 sealed class ConstructorConstraint<T> where T : new() 223 { 224 public static T Factory() 225 { 226 return new T(); 227 } 228 } 229 230 //12.8.4 其他可驗證性問題 231 //1). 泛型的類型轉換 232 static void Test6<T>(T obj) 233 { 234 //編譯錯誤 235 //int x = (int)obj; 236 //string s = (string)obj; 237 } 238 239 static void Test7<T>(T obj) 240 { 241 //可通過編譯，但可能出現運行時異常 242 int x = (int)(object)obj; 243 string s = (string)(object)obj; 244 } 245 246 static void Test8<T>(T obj) 247 { 248 //無錯誤 249 string s = obj as string; 250 } 251 252 //2). 泛型初始化 253 static void Test9<T>() 254 { 255 //T temp = null; 256 T temp = default(T); 257 } 258 259 } 260 }
讀書筆記：CLR var C# 第12章