在IEnumerable的情况下使用System.Linq <t> ？

Question

I have an API which returns System.Collections.Generic.IEnumerable<t> , if I import( using ) System.Linq . I am able to do Count() / ToList() on the returned object.

What would be the relation between those two( System.Collections.Generic , System.Linq ), packages ?

Thanks Pavan

Answer 1

IEnumerable<> is that relationship. Those methods (Count(), ToList()) are extension methods on IEnumerable<>

This means that anything that implements IEnumerable (IList, ICollection, Arrays) they all will have those methods. To use them you need to "import" those methods with Using System.Linq; statement

A simple extension method on String. can be

public static class StringExtensions 
{
    public static string CountWords(this string input )
    {
         return imnput.Split(new char[]{' '}).Length;
    }
}

Answer 2

System.Linq命名空间中有一个静态类Enumerable ，它提供了与IEnumerable<T>类型一起使用的大多数扩展方法。