IsAssignableFrom，IsInstanceOfType和是关键字，有什么区别？ [英] IsAssignableFrom, IsInstanceOfType and the is keyword, what is the difference?

问题描述

我有一个安全的投放对象的扩展方法，如下所示：

I have an extension method to safe casting objects, that looks like this:

public static T SafeCastAs<T>(this object obj) {
    if (obj == null)
        return default(T);

    // which one I should use?

    // 1. IsAssignableFrom
    if (typeof(T).IsAssignableFrom(obj.GetType()))
        return (T)obj;

    // 2. IsInstanceOfType
    if (typeof(T).IsInstanceOfType(obj))
        return (T) obj;

    // 3. is operator
    if (obj is T)
        return (T) obj;

    return default(T);
}

如你所见，我有3个选择，使用？实际上 IsAssignableFrom ， IsInstanceOfType 和之间的区别是运算符？

推荐答案

您可以使用任何您拥有的信息。

You use whatever you have the information for.

您有一个要检查的实例和静态类型，请使用是

If you have an instance and a static type you want to check against, use is.

具有静态类型，你只有一个类型对象，但你有一个要检查的实例，使用 IsInstanceOfType 。

If you don't have the static type, you just have a Type object, but you have an instance you want to check, use IsInstanceOfType.

如果您没有实例，而只想检查类型和另一个类型，请使用 IsAssignableFrom 。

If you don't have an instance and you just want to check the compatibility between a theoretical instance of a Type and another Type, use IsAssignableFrom.

但实际上似乎你只是重新实现作为operator < a>（除了你的也可以用于不可为null的值类型，这通常不是一个大的限制）。

But really is seems like you are just re-implementing the as operator (except that yours would also work for non-nullable value types, which is usually not a big limitation).

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