更新时间:2022-10-17 23:36:38
不能用一个具体的实现覆盖泛型方法;这不是泛型的工作原理。例如, Extended
类必须能够处理对 GetSomething< int>()
的调用。 b
$ b
换句话说,重写方法的签名必须与它重写的方法相同。通过指定该方法的具体通用实现,您可以更改其签名。
考虑使用此方法:
public override T GetSomething< T>()
{
if(typeof(T)== typeof(string))
return string.Empty;
return base.GetSomething< T>();
$ / code>
请注意,JIT应该在编译此特定实例时优化条件方法。 (如果它没有,那么它不是一个很好的JIT!)
(你的覆盖的语法在技术上是正确的,但是由于其他原因也失败了。 ,你不能使用关键字 string
作为通用参数名,如果可以的话,你的代码仍然不会做你想要的,也不会编译它,因为编译器将无法在超类型上找到具有该签名的方法。)
There is a base class which has one method of generic type and I am sure that in my derived I will be returning a string. This is my code:
public abstract class Base
{
public virtual T GetSomething<T>()
{
return default(T);
}
}
public class Extended : Base
{
public override string GetSomething<string>()
{
return string.Empty;
//return base.GetSomething<T>();
}
}
But this code doesn't compile. Can anybody spot the mistake? I am sure that in my Extended class I want to return string only. How do I solve this?
You cannot override a generic method with a concrete implementation; that's not how generics work. The Extended
class must be able to handle calls to GetSomething<int>()
for example.
In other words, the signature for an overriding method must be identical to the method it is overriding. By specifying a concrete generic implementation of the method, you change its signature.
Consider using this approach:
public override T GetSomething<T>()
{
if (typeof(T) == typeof(string))
return string.Empty;
return base.GetSomething<T>();
}
Note that the JIT should optimize away the conditional when compiling a particular instantiation of this method. (If it doesn't then it's not a very good JIT!)
(The syntax for your override is technically correct, but fails for other reasons as well. For example, you can't use the keyword string
as a generic parameter name. And if you could, your code still wouldn't do what you want, nor would it compile, since the compiler would be unable to find a method with that signature on a supertype.)