docs/csharp/language-reference/statements/snippets/yield/Program.cs - main - aprogrammer/dotnet-docs

docs/csharp/language-reference/statements/snippets/yield/Program.cs
118 строк3 KB
Dipendra Shah
Update Program.cs (#40826)
09 май 2024, 16:45
09 май 2024, 16:45ce44a46
YieldReturn();
YieldBreak();
await IteratorAsync();
GetEnumeratorExample.Example();
Console.WriteLine();
IteratorExecution();

static void YieldReturn()
{
    // <YieldReturn>
    foreach (int i in ProduceEvenNumbers(9))
    {
        Console.Write(i);
        Console.Write(" ");
    }
    // Output: 0 2 4 6 8

    IEnumerable<int> ProduceEvenNumbers(int upto)
    {
        for (int i = 0; i <= upto; i += 2)
        {
            yield return i;
        }
    }
    // </YieldReturn>
    Console.WriteLine();
}

static void YieldBreak()
{
    // <YieldBreak>
    Console.WriteLine(string.Join(" ", TakeWhilePositive(new int[] {2, 3, 4, 5, -1, 3, 4})));
    // Output: 2 3 4 5

    Console.WriteLine(string.Join(" ", TakeWhilePositive(new int[] {9, 8, 7})));
    // Output: 9 8 7

    IEnumerable<int> TakeWhilePositive(IEnumerable<int> numbers)
    {
        foreach (int n in numbers)
        {
            if (n > 0)
            {
                yield return n;
            }
            else
            {
                yield break;
            }
        }
    }
    // </YieldBreak>
}

static async Task IteratorAsync()
{
    // <IteratorAsync>
    await foreach (int n in GenerateNumbersAsync(5))
    {
        Console.Write(n);
        Console.Write(" ");
    }
    // Output: 0 2 4 6 8

    async IAsyncEnumerable<int> GenerateNumbersAsync(int count)
    {
        for (int i = 0; i < count; i++)
        {
            yield return await ProduceNumberAsync(i);
        }
    }

    async Task<int> ProduceNumberAsync(int seed)
    {
        await Task.Delay(1000);
        return 2 * seed;
    }
    // </IteratorAsync>
    Console.WriteLine();
}

static void IteratorExecution()
{
    // <IteratorExecution>
    var numbers = ProduceEvenNumbers(5);
    Console.WriteLine("Caller: about to iterate.");
    foreach (int i in numbers)
    {
        Console.WriteLine($"Caller: {i}");
    }

    IEnumerable<int> ProduceEvenNumbers(int upto)
    {
        Console.WriteLine("Iterator: start.");
        for (int i = 0; i <= upto; i += 2)
        {
            Console.WriteLine($"Iterator: about to yield {i}");
            yield return i;
            Console.WriteLine($"Iterator: yielded {i}");
        }
        Console.WriteLine("Iterator: end.");
    }
    // Output:
    // Caller: about to iterate.
    // Iterator: start.
    // Iterator: about to yield 0
    // Caller: 0
    // Iterator: yielded 0
    // Iterator: about to yield 2
    // Caller: 2
    // Iterator: yielded 2
    // Iterator: about to yield 4
    // Caller: 4
    // Iterator: yielded 4
    // Iterator: end.
    // </IteratorExecution>
    Console.WriteLine();
}