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  • C#中的协变OUT和逆变

    泛型接口和泛型委托中经常使用可变性

     in  逆变,out  协变

    从 list<string>转到list<object> 称为协变 (string 从object 派生,那么 string 转成object 是合理的,子类替换父类是合理的,)

    从list<object> 转到 list<string> 称为逆变 (经object 转成string ,将父类转成子类,是不合理的,称为逆变)

    1.逆变代码掩饰

      static void Main(string[] args)
            {
                ICovariant<Object> iobj = new Sample<Object>();
                ICovariant<String> istr = new Sample<String>();
    
                // You can assign istr to iobj because
                // the ICovariant interface is covariant.
               // iobj = istr;
                istr = iobj; //从 object 类型转成string 类型,父类转成子类 则是逆变
                Console.ReadLine();
            }
    
            // Covariant interface.
            interface ICovariant<in R> { }
    
            // Extending covariant interface.
            interface IExtCovariant<in R> : ICovariant<R> { }
    
            // Implementing covariant interface.
            class Sample<R> : ICovariant<R> { }

    2.协变演示

       static void Main(string[] args)
            {
                ICovariant<Object> iobj = new Sample<Object>();
                ICovariant<String> istr = new Sample<String>();
    
                // You can assign istr to iobj because
                // the ICovariant interface is covariant.
               // iobj = istr;
                iobj = istr; //从 string类型转成object类型,子类型转成父类  (里氏替换原则)  则是协变
                Console.ReadLine();
            }
    
            // Covariant interface.
            interface ICovariant<out R> { }
    
            // Extending covariant interface.
            interface IExtCovariant<out R> : ICovariant<R> { }
    
            // Implementing covariant interface.
            class Sample<R> : ICovariant<R> { }
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  • 原文地址:https://www.cnblogs.com/tiancai/p/4761206.html
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