通用方法和类型转换

Question

我阅读了以下问题（我将按照给定答案的相同方式解决）：

但为什么无法从派生的 class 中找到 value 属性？即使我添加类型转换也是不可能的：

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;
}

带有类型转换的示例也不起作用（显示了冗余类型转换的建议）：

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

因为您要在方法上声明泛型类型参数。编译器不理解这应该是 derived 类型。它只知道您引入了一个新的泛型类型参数。

你想要的叫做F-bound polymorphism，其中类型参数是实现class，递归定义：

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; }
}

通用方法和类型转换

Generic methods and type casting

c#

generics

generic-method