泛型方法和类型转换

Question

我读了以下问题（我会解决这个问题的相同的方式给出答案）：Passing derived type as argument to abstract class

但为什么不能找到派生类中的value属性？即使我添加一个类型转换是不可能的：

public abstract class baseClass 
{ 
    public abstract float function<T>(T a, T b) where T:baseClass; 
} 

public class derived: baseClass 
{ 
    public override float function<derived>(derived a, derived b) 
    { 
     // Here value is not found 
     return a.value + b.value; 
    } 

    public float value; 
} 

实例与类型转换也没有工作（和建议冗余类型转换所示）：

public abstract class baseClass 
{ 
    public abstract float function<T>(T a, T b) where T:baseClass; 
} 

public class derived: baseClass 
{ 
    public override float function<derived>(derived a, derived b) 
    { 
     // Here value is not found even with type cast 
     return ((derived)a).value + ((derived)b).value; 
    } 

    public float value; 
} 

Answer 1

因为你声明该方法的泛型类型参数。编译器不明白这应该是derived类型。它只知道你已经引入了一个新的泛型类型参数。

你想要什么叫做F-bound polymorphism，其中类型参数是实现类，递归定义的：

public abstract class BaseClass<T> where T : BaseClass<T> 
{ 
    public abstract float Function(T a, T b); 
} 

public class Derived : BaseClass<Derived> 
{ 
    public override float Function(Derived a, Derived b) 
    { 
     return a.Value + b.Value; 
    } 

    public float Value { get; set; } 
}