提前终止

你可以通过调用 yield break 来传递一个或多个可以在函数中定义终止条件的值或元素来扩展现有 yield 方法的功能，以阻止内循环执行。

public static IEnumerable<int> CountUntilAny(int start, HashSet<int> earlyTerminationSet)
{
    int curr = start;

    while (true)
    {
        if (earlyTerminationSet.Contains(curr))
        {
            // we've hit one of the ending values
            yield break;
        }

        yield return curr;

        if (curr == Int32.MaxValue)
        {
            // don't overflow if we get all the way to the end; just stop
            yield break;
        }

        curr++;
    }
}

上述方法将从给定的 start 位置迭代，直到遇到 earlyTerminationSet 中的一个值。

// Iterate from a starting point until you encounter any elements defined as 
// terminating elements
var terminatingElements = new HashSet<int>{ 7, 9, 11 };
// This will iterate from 1 until one of the terminating elements is encountered (7)
foreach(var x in CountUntilAny(1,terminatingElements))
{
    // This will write out the results from 1 until 7 (which will trigger terminating)
    Console.WriteLine(x);
}

输出：

1
2
3
4
5
6

.NET 小提琴现场演示