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【C#补全计划】泛型约束

backend 2025/8/26 8:58:57

一、泛型约束的概念

1. 作用：让泛型的类型有一定的限制

2. 关键字：where

3. 种类：6种

（1）值类型： struct

（2）引用类型：class

（3）无参的公共构造函数：new()

（4）某个类本身或其派生类：类名

（5）某个接口的派生类：接口名

（6）另一个泛型类本身或其派生类型：其他泛型

4. 语法：where 泛型 : 种类

二、泛型约束的使用

1. 值类型

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}
}

2. 引用类型

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}
}

3. 存在公共的无参构造函数

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}
}

4. 是某个类本身或其派生类

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());// Test4<Test1<int>> t4 = new Test4<Test1<int>>(); 编译报错：因为Test4是Test2或其子类约束，而Test1不是Test2或其子类Test4<Test2<object>> t4 = new Test4<Test2<object>>();t4.fun(new Test2<object>());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}class Test4<T> where T : Test2<object>{public T value;public void fun<K>(K k) where K : Test2<object>{Console.WriteLine(k + "是Test2类或其派生类");}}
}

5. 是某个接口的派生类型

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());// Test4<Test1<int>> t4 = new Test4<Test1<int>>(); 编译报错：因为Test4是Test2或其子类约束，而Test1不是Test2或其子类Test4<Test2<object>> t4 = new Test4<Test2<object>>();t4.fun(new Test2<object>());// Test5<A> t5 = new Test5<A>(); 编译报错：因为Test5是ITest接口实现类约束，而A没有实现ITest接口Test5<C> t5 = new Test5<C>();t5.fun(new C());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}class Test4<T> where T : Test2<object>{public T value;public void fun<K>(K k) where K : Test2<object>{Console.WriteLine(k + "是Test2类或其派生类");}}// 接口约束class Test5<T> where T : ITest{public T value;public void fun<K>(K k) where K : ITest{Console.WriteLine(k + "是ITest接口的派生类");}}interface ITest { }class C : ITest { }
}

6. 是另一个泛型类本身或其派生类型

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());// Test4<Test1<int>> t4 = new Test4<Test1<int>>(); 编译报错：因为Test4是Test2或其子类约束，而Test1不是Test2或其子类Test4<Test2<object>> t4 = new Test4<Test2<object>>();t4.fun(new Test2<object>());// Test5<A> t5 = new Test5<A>(); 编译报错：因为Test5是ITest接口实现类约束，而A没有实现ITest接口Test5<C> t5 = new Test5<C>();t5.fun(new C());// Test6<C, E> t6 = new Test6<C, E>(); 编译报错：因为Test6是另一个泛型类或及其派生类约束，而C不是E或其派生类Test6<D, E> t6 = new Test6<D, E>();t6.fun<D, E>(new D());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}class Test4<T> where T : Test2<object>{public T value;public void fun<K>(K k) where K : Test2<object>{Console.WriteLine(k + "是Test2类或其派生类");}}// 接口约束class Test5<T> where T : ITest{public T value;public void fun<K>(K k) where K : ITest{Console.WriteLine(k + "是ITest接口的派生类");}}interface ITest { }class C : ITest { }// 泛型类及其派生类约束class Test6<T, M> where T : M{public T value;public void fun<K, V>(K k) where K : V{Console.WriteLine(k + "是" + typeof(V) + "或其派生类");}}class E { }class D : E { }
}

运行结果如下：

三、泛型有多个约束

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());// Test4<Test1<int>> t4 = new Test4<Test1<int>>(); 编译报错：因为Test4是Test2或其子类约束，而Test1不是Test2或其子类Test4<Test2<object>> t4 = new Test4<Test2<object>>();t4.fun(new Test2<object>());// Test5<A> t5 = new Test5<A>(); 编译报错：因为Test5是ITest接口实现类约束，而A没有实现ITest接口Test5<C> t5 = new Test5<C>();t5.fun(new C());// Test6<C, E> t6 = new Test6<C, E>(); 编译报错：因为Test6是另一个泛型类或及其派生类约束，而C不是E或其派生类Test6<D, E> t6 = new Test6<D, E>();t6.fun<D, E>(new D());Test7<B> t7 = new Test7<B>();t7.fun(new B());}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}class Test4<T> where T : Test2<object>{public T value;public void fun<K>(K k) where K : Test2<object>{Console.WriteLine(k + "是Test2类或其派生类");}}// 接口约束class Test5<T> where T : ITest{public T value;public void fun<K>(K k) where K : ITest{Console.WriteLine(k + "是ITest接口的派生类");}}interface ITest { }class C : ITest { }// 泛型类及其派生类约束class Test6<T, M> where T : M{public T value;public void fun<K, V>(K k) where K : V{Console.WriteLine(k + "是" + typeof(V) + "或其派生类");}}class E { }class D : E { }// 泛型有多个约束：使用逗号分隔class Test7<T> where T : class, new(){public T value;public void fun<K>(K k) where K : class, new(){Console.WriteLine(k + "是引用类型且有公共无参构造方法");}}
}

运行结果如下：

四、多个泛型有约束

using System;namespace GenericConstraints
{class Program{static void Main(string[] args){// Test<object> t1 = new Test<object>(); 编译报错：因为Test1是值类型约束，而object是引用类型Test1<int> t1 = new Test1<int>();t1.fun(123);// Test2<int> t2 = new Test2<int>(); 编译报错：因为Test2是引用类型约束，而int是值类型Test2<object> t2 = new Test2<object>();t2.fun(new Random());// Test3<A> t3 = new Test3<A>(); 编译报错：因为Test3是无参公共构造函数约束，而A没有公共无参构造函数Test3<B> t3 = new Test3<B>();t3.fun(new B());// Test4<Test1<int>> t4 = new Test4<Test1<int>>(); 编译报错：因为Test4是Test2或其子类约束，而Test1不是Test2或其子类Test4<Test2<object>> t4 = new Test4<Test2<object>>();t4.fun(new Test2<object>());// Test5<A> t5 = new Test5<A>(); 编译报错：因为Test5是ITest接口实现类约束，而A没有实现ITest接口Test5<C> t5 = new Test5<C>();t5.fun(new C());// Test6<C, E> t6 = new Test6<C, E>(); 编译报错：因为Test6是另一个泛型类或及其派生类约束，而C不是E或其派生类Test6<D, E> t6 = new Test6<D, E>();t6.fun<D, E>(new D());Test7<B> t7 = new Test7<B>();t7.fun(new B());Test8<int, object> t8 = new Test8<int, object>();t8.fun(666, "Hello World!");}}// 值类型class Test1<T> where T : struct{public T value;public void fun<K>(K k) where K : struct{Console.WriteLine(k + "是值类型");}}// 引用类型class Test2<T> where T : class{public T value;public void fun<K>(K k) where K : class{Console.WriteLine(k + "是引用类型");}}// 存在公共无参构造函数class Test3<T> where T : new(){public T value;public void fun<K>(K k) where K : new(){Console.WriteLine(k + "有公共无参构造方法");}}class A{private int value;public A(int value){this.value = value;}}class B{public B() {}}class Test4<T> where T : Test2<object>{public T value;public void fun<K>(K k) where K : Test2<object>{Console.WriteLine(k + "是Test2类或其派生类");}}// 接口约束class Test5<T> where T : ITest{public T value;public void fun<K>(K k) where K : ITest{Console.WriteLine(k + "是ITest接口的派生类");}}interface ITest { }class C : ITest { }// 泛型类及其派生类约束class Test6<T, M> where T : M{public T value;public void fun<K, V>(K k) where K : V{Console.WriteLine(k + "是" + typeof(V) + "或其派生类");}}class E { }class D : E { }// 泛型有多个约束：使用逗号分隔class Test7<T> where T : class, new(){public T value;public void fun<K>(K k) where K : class, new(){Console.WriteLine(k + "是引用类型且有公共无参构造方法");}}// 多个泛型有约束：多条where语句class Test8<T, M> where T : struct where M : class{public T value;public void fun<K, V>(K k, V v) where K : struct where V : class{Console.WriteLine(k + "是值类型且" + v + "是引用类型");}}
}

运行结果如下：