从静态基类方法调用子类构造函数 [英] Calling subclass constructor from static base class method

问题描述

好吧……在目标C中，您可以使用 new this（）从基类的静态方法中创建一个子类，因为在静态方法中， this是指该类，而不是实例。当我第一次发现它并且经常使用它时，这真是一个非常酷的发现。

Ok... in Objective C you can new up a subclass from a static method in the base class with 'new this()' because in a static method, 'this' refers to the class, not the instance. That was a pretty damn cool find when I first found it and I've used it often.

但是，在C＃中不起作用。

However, in C# that doesn't work. Damn!

所以...有人知道我如何从静态基类方法中新建一个子类吗？

So... anyone know how I can 'new' up a subclass from within a static base class method?

类似这样的事情……

public class MyBaseClass{

    string name;

    public static Object GimmeOne(string name){

     // What would I replace 'this' with in C#?
        return new this(name); 

    }

    public MyBaseClass(string name){
        this.name = name;
    }

}

// No need to write redundant constructors
   public class SubClass1 : MyBaseClass{ }
   public class SubClass2 : MyBaseClass{ }
   public class SubClass3 : MyBaseClass{ }

SubClass1 foo = SubClass1.GimmeOne("I am Foo");

是的，我知道我可以（并且通常会）直接使用构造函数，但是我们有在基类上调用共享成员的特定需求，这就是我要问的原因。同样，目标C让我执行此操作。希望C＃也是。

And yes, I know I can (and normally would) just use the constructors directly, but we have a specific need to call a shared member on the base class so that's why I'm asking. Again, Objective C let's me do this. Hoping C# does too.

所以...有任何人吗？

So... any takers?

推荐答案

C＃没有与此完全相同的东西。但是，您可以通过使用如下通用类型约束来解决此问题：

C# doesn't have any exact equivalent to that. However, you could potentially get around this by using generic type constraints like this:

public class MyBaseClass
{
    public string Name { get; private set; }

    public static T GimmeOne<T>(string name) where T : MyBaseClass, new()
    {
        return new T() { Name = name };
    }

    protected MyBaseClass()
    {
    }

    protected MyBaseClass(string name)
    {
        this.Name = name;
    }
}

new（）约束表示存在无参数构造函数-您没有这么做，但我们将其隐藏起来以向消费者隐藏。然后可以像这样调用它：

The new() constraint says there is a parameterless constructor - which your didn't but we make it private to hide that from consumers. Then it could be invoked like this:

var foo = SubClass1.GimmeOne<SubClass1>("I am Foo");

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