问题描述
我有一个类Animal，以及它的子类Dog.我有一个 List<Animal>，我想将一些 List<Dog> 的内容添加到 List<Animal>.除了将 List<Dog> 转换为 List<Animal>，然后使用 AddRange 之外，有没有更好的方法呢?
I have a class Animal, and its subclass Dog.
I have a List<Animal> and I want to add the contents of some List<Dog> to the List<Animal>.
Is there a better way to do so, than just cast the List<Dog> to a List<Animal>, and then use AddRange?
推荐答案
如果您使用 C#4，则不需要强制转换:
You don't need the cast if you're using C#4:
List<Animal> animals = new List<Animal>();
List<Dog> dogs = new List<Dog>();
animals.AddRange(dogs);
这是允许的，因为 AddRange() 接受 IEnumerable<T>，即 协变.
That's allowed, because AddRange() accepts an IEnumerable<T>, which is covariant.
但是，如果您没有 C#4，那么您将不得不迭代 List<Dog> 并强制转换每个项目，因为那时才添加协方差.您可以通过 .Cast<T> 扩展方法完成此操作:
If you don't have C#4, though, then you would have to iterate the List<Dog> and cast each item, since covariance was only added then. You can accomplish this via the .Cast<T> extension method:
animals.AddRange(dogs.Cast<Animal>());
如果您甚至没有 C#3.5，那么您将不得不手动进行转换.
If you don't even have C#3.5, then you'll have to do the casting manually.
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