Returns the head of a collection.

Use IEnumerable.Count() to check if the enumerable is non-empty.
Use IEnumerable.Take(1) to get the first element, IEnumerable.ToArray()[0] to convert to array and return the element.
If the enumerable object is empty, return the default() value for the given type.

代码实现

using System.Collections.Generic;
using System.Linq;

public static partial class _30s 
{
  public static T Head<T>(IEnumerable<T> list) 
  {
    return list.Count() != 0 ? list.Take(1).ToArray()[0] : default(T);
  }
}

使用样例

List<int> nums = new List<int> { 1, 2, 3, 4, 5 };
List<int> empty = new List<int> { };
char[] chars = {'A','B','C'};

_30s.Head(nums); // 1
_30s.Head(empty); // 0
_30s.Head(chars); // 'A'