186 lines
4.2 KiB
C#
186 lines
4.2 KiB
C#
namespace Lesson6_泛型约束
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{
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#region 知识回顾
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//泛型类
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class TestClass<T, U>
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{
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public T t;
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public U u;
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public U TestFun(T t)
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{
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return default(U);
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}
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//泛型函数
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public V TestFun<K, V>(K k)
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{
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return default(V);
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}
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}
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#endregion
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#region 知识点一 什么是泛型约束
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//让泛型的类型有一定限制
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//关键字：where
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//泛型约束一共有6种
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//1.值类型 where 泛型字母：struct
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//2.引用类型 where 泛型字母：class
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//3.存在无参公共构造函数 where 泛型字母：new()
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//4.某个类本身或其派生类 where 泛型字母：类名
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//5.某个接口的派生类 where 泛型字母：接口名
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//6.另一个泛型类本身或派生类 where 泛型字母：另一个泛型字母
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#endregion
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#region 知识点二 各泛型约束讲解
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class Test1<T> where T : struct
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{
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public T v;
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public void TestFun<K>(K v) where K : struct
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{
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}
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}
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class Test2<T> where T : class
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{
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public T value;
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public void TestFun<K>(K v) where K : class
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{
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}
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}
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class Test3<T> where T: new()
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{
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public T value;
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public void TestFun<K>(K v) where K : new()
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{
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}
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}
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class Test1
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{
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}
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class Test2
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{
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public Test2(int i)
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{
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}
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}
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class Test4<T> where T : Test1
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{
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public T value;
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public void TestFun<K>(K v) where K : Test1
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{
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}
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}
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class Test3 : Test1
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{
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}
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interface IFly
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{
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}
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class Test4 : IFly
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{
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}
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class Test5<T> where T : IFly
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{
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public T value;
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public void TestFun<K>(K v) where K : IFly
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{
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}
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}
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class Test6<T,U> where T : U
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{
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public T value;
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public void TestFun<K,V>(K k) where K : V
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{
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}
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}
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#endregion
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#region 知识点三 约束的组合使用
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class Test7<T> where T : class, new()
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{
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}
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#endregion
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#region 知识点四 多个泛型有约束
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class Test8<T,K> where T:class,new() where K : struct
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{
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}
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#endregion
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#region 总结
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//泛型约束: 让类型有一定限制
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//class
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//struct
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//new()
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//类名
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//接口名
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//另一个泛型字母
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//注意:
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//1.可以组合使用
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//2.多个泛型约束 用where连接即可
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#endregion
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internal class Program
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{
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static void Main(string[] args)
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{
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TestClass<string,int> t = new TestClass<string,int>();
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t.t = "123fgd";
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t.u = 10;
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t.TestFun("123");
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t.TestFun<float,double>(123);
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//Test1<Object> t1 = new Test1<object>;//Object类型不能为空，所以报错
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Test1<int> t1 = new Test1<int>();//int是值类型，所以可以放
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//t1.TestFun<Random>();//不可为空同样报错
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t1.TestFun<float>(1.3f);
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//Test2<int> t2 = new Test2<int>;//因为是引用类型所以值类型int会报错
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Test2<Random> t2 = new Test2<Random>();
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t2.TestFun<string>("123");
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t2.TestFun<Object>(new object());
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t2.value = new Random();
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Test3<Test1> t3 = new Test3<Test1>();//如果Test1的构造函数是私有也会报错
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//Test3<Test2> t4 = new Test3<Test2>();//test2有参所以报错，如果test2是无参但抽象类也会报错，必须是有公共无参构造函数的非抽象类
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//Test3<int> t4 = new Test3<int>();//没问题，struct值类型是默认有无参构造且不会被顶替的
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Test4<Test3> t4 = new Test4<Test3>();//Test3是继承约束的Test1的类，所以也不会报错
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Test5<IFly> t5 = new Test5<IFly>();
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t5.value = new Test4();//继承IFly的Test4
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Test6<Test4,IFly> t6 = new Test6<Test4, IFly> ();
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Test6<Test4, Test4> tx = new Test6<Test4, Test4>();
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}
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}
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}
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