深入了解c# 迭代器和列举器

IEnumerable<int> Fibonacci(int count)
{
 int prev = 1;
 int curr = 1;
 for (int i = 0; i < count; i++)
 {
 yield return prev;
 int temp = prev + curr;
 prev = curr;
 curr = temp;
 }
}

void Main()
{
 foreach (int term in Fibonacci(10))
 {
 Console.WriteLine(term);
 }
}

int[] numbers = { 1, 2, 3, 4, 5 };
IEnumerator enumerator = numbers.GetEnumerator();
while (enumerator.MoveNext())
{
 Console.WriteLine(enumerator.Current);
}

int[] numbers = { 1, 2, 3, 4, 5 };
foreach (int number in numbers)
{
 Console.WriteLine(number);
}

public class CoffeeCollection : IEnumerable
{
 private CoffeeEnumerator enumerator;
 public CoffeeCollection()
 {
 enumerator = new CoffeeEnumerator();
 }

 public IEnumerator GetEnumerator()
 {
 return enumerator;
 }

 public class CoffeeEnumerator : IEnumerator
 {
 string[] items = new string[3] { "espresso", "macchiato", "latte" };
 int currentIndex = -1;
 public object Current
 {
 get
 {
 return items[currentIndex];
 }
 }
 public bool MoveNext()
 {
 currentIndex++;
 if (currentIndex < items.Length)
 {
 return true;
 }
 return false;
 }
 public void Reset()
 {
 currentIndex = 0;
 }
 }
}

public static void Main(string[] args)
{
 foreach (var coffee in new CoffeeCollection())
 {
 Console.WriteLine(coffee);
 }
}

if(enumerable.Count() > 0)
{
 // 集合中有元素
}

if(enumerable.GetEnumerator().MoveNext())
{
 // 集合中有元素
}

if(enumerable.Any())
{
 // 集合中有元素
}