在这种特殊情况下，使用的IEnumerable< T> 的形式会更有效率，因为你的只有的需要知道计数。有没有点中存储数据，调整缓冲区等，如果你不需要。

In this particular case, using the IEnumerable<T> form will be more efficient, because you only need to know the count. There's no point in storing the data, resizing buffers etc if you don't need to.

如果您需要再次使用该结果以任何理由，在列表< T> 的形式会更有效。

If you needed to use the results again for any reason, the List<T> form would be more efficient.

请注意，无论是 COUNT（）扩展方法和计数属性将是有效的列表< T> 的实施计数（）检查是否目标序列实现的ICollection< T> ，并使用计数财产，如果左右。

Note that both the Count() extension method and the Count property will be efficient for List<T> as the implementation of Count() checks to see if the target sequence implements ICollection<T> and uses the Count property if so.

这应该是另一种选择，甚至的更多的高效（虽然只是刚）将调用过载计数这需要一个委托：

Another option which should be even more efficient (though only just) would be to call the overload of Count which takes a delegate:

private int GetProviderCount(Type type)
{
  return _objectProviders.Count(provider =>
      (provider.Key.IsAssignableFrom(type) 
       || type.IsAssignableFrom(provider.Key))
      && provider.Value.SupportsType(type));
}

这将避免由其中，和选择条款。

（正如马克说，对于少量的数据的性能差异可能是微不足道的反正。）

(As Marc says, for small amounts of data the performance differences will probably be negligible anyway.)