在C＃中定义泛型的显式转换 [英] Defining explicit casting for generic types in C#

问题描述

作为练习的一部分，我试图为泛型类定义与特定类型一起使用时的特定行为。更确切地说，我想知道是否可以为泛型类型定义显式转换运算符，即从 list< T> 到 int []

As part of an exercise I am trying to define a specific behavior for a generic class when used with a specific type. More precisely, I was wondering if it is possible to define a explicit casting operator for a generic type, i.e. from list<T> to int[]

不，我知道我可以简单地定义一个可以完成工作的方法，但这不是练习的目的。

No, I know I could simply define a method that does the work, however this is not the goal of the exercise.

假设通用类 list< T> 我试图定义以下显式转换方法

Assuming the generic class list<T> I was trying to define the following explicit casting method

class list<T> {
...

    public static explicit operator int[](list<T> _t) where T : System.Int32 
    {
        // code handling conversion from list<int> to int[]
    }
}

但这是行不通的。有什么想法可以使编译器吞并这个？

This doesn't work however. Any ideas on how to make the compiler swallow this?

推荐答案

首先，请更改名称遵循.NET约定和的类，避免与 List< T> 冲突。

Firstly, please change the name of the class to follow .NET conventions and avoid clashing with List<T>.

因此，您基本上无法做您想做的事情。您可以定义一个对 all T 有效的转换，然后针对不同的情况采取不同的措施。因此，您可以这样写：

With that out of the way, you basically can't do what you're trying to do. You can define a conversion which is valid for all T, and then take different action for different cases. So you could write:

public static explicit operator T[](CustomList<T> input)

然后如果 T 是 int则区别对待。进行最后一部分并不是很好，但是如果您确实想要的话也可以这样做。

and then treat this differently if T is int. It wouldn't be nice to do the last part, but you could do it if you really wanted.

特定泛型类型上可用的成员是相同的，无论类型参数（在类型参数声明时声明的约束内）-否则它不是真正的泛型。

The members available on a particular generic type are the same whatever the type arguments (within the constraints declared at the point of type parameter declaration) - otherwise it's not really generic.

作为替代方案，您可以在顶部定义扩展方法级别的静态非一般类型：

As an alternative, you could define an extension method in a top-level static non-generic type elsewhere:

public static int[] ToInt32Array(this CustomList<int> input)
{
    ...
}

这将允许您编写：

CustomList<int> list = new CustomList<int>();
int[] array = list.ToInt32Array();

我个人还是觉得它比显式转换运算符更清楚。

Personally I'd find that clearer than an explicit conversion operator anyway.

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