转换Template类的类型？

I have a class named "baseClass". From this class I inherit a class names "inheritedClass" (public class inheritedClass: baseClass)

我有一个名为“baseClass”的类。从这个类我继承了一个类名“inheritedClass”(公共类inheritedClass:baseClass)

The baseClass contains a public function that returns a HashSet<baseClass>. When called from the inheritedClass, the return type is obviously still HashSet<baseClass>, but I need a HashSet<inheritedClass>.

baseClass包含一个返回HashSet 的公共函数。从inheritedClass调用时,返回类型显然仍然是HashSet ,但我需要一个HashSet 。

A conversion ala (HashSet<inheritedClass>)returnValue, where returnValue is of Type HashSet<baseClass> doesn't work.

转换ala(HashSet )returnValue,其中returnValue属于Type HashSet 不起作用。

Is there a way to convert the HashSet-Type from baseClass to inheritedClass without converting each element manually?

有没有办法将HashSet-Type从baseClass转换为inheritedClass而不手动转换每个元素?

Thanks in advance, Frank

先谢谢你,弗兰克

2 个解决方案

#1

Do you really mean C# in the tags? HashMap is a Java type. Also it generally has two type parameters rather than one...

你真的是指标签中的C#吗? HashMap是一种Java类型。它通常有两个类型参数而不是一个......

In C#, generic classes are always invariant. Some interfaces will be variant in C# 4, but very few (only those which either only use the type parameter in an output positiion, e.g. IEnumerable<T>, or only use the type parameter in an input position, e.g. IComparable<T>).

在C#中,泛型类总是不变的。有些接口在C#4中是变体的,但很少(只有那些只在输出位置使用type参数的接口,例如IEnumerable ,或者只在输入位置使用type参数,例如IComparable ) 。

If you can provide more precise information about your situation, we'll probably be able to help come up with a simple solution - particularly if you can use LINQ with its Cast<T>() method.

如果您可以提供有关您的情况的更准确信息,我们可能会帮助提出一个简单的解决方案 - 特别是如果您可以使用LINQ及其Cast ()方法。

EDIT: Okay, with HashSet<T>:

编辑:好的,使用HashSet :

HashSet<BaseType> baseSet = ...;
var derivedSet = new HashSet<DerivedType>(baseSet.Cast<DerivedType>());

Note that even with C# 4 this would be necessary because the compiler doesn't know that every value in baseSet is an instance of DerivedType - there has to be an execution-time check. The reverse (creating a HashSet<BaseType> from a HashSet<DerivedType>) would work in C# 4.

请注意,即使使用C#4,这也是必要的,因为编译器不知道baseSet中的每个值都是DerivedType的实例 - 必须进行执行时检查。反向(从HashSet 创建HashSet )将在C#4中起作用。

FURTHER EDIT: If you just want to use UnionWith, that doesn't require a HashSet<DerivedType> - it requires an IEnumerable<DerivedType>. I suggest you do:

进一步编辑:如果您只想使用UnionWith,那不需要HashSet - 它需要IEnumerable 。我建议你这样做:

HashSet<BaseType> baseSet = ...;
HashSet<DerivedType> derivedSet = ...;

derivedSet.UnionWith(baseSet.Cast<DerivedType>());

#2

Here's the solution

这是解决方案

//**Your BaseClass**
public class BaseClass<T> where T : BaseClass<T>
{
    public HashSet<T> GetHashSet()
    {
        HashSet<T> _hSet = new HashSet<T>();
        //do some work              
        //create a HashSet<T> and return;              
        return _hSet;
    }
}
//**Your Inherited/Derived Class**
public class InheritedClass : BaseClass<InheritedClass>
{
    //you have the method inherited as you need.}
}

#1