C# Async Streams

AsyncEnumerator.cs

IAsyncEnumerator<int> e = GetNumbers().GetAsyncEnumerator();
while (await e.MoveNextAsync())
{
    Console.WriteLine($"取得 {e.Current}");
}

enum-yield-return.cs

IEnumerable<int> numbers = GetNumbers();
foreach (int n in numbers)
{
    Console.WriteLine($"取得 {n}");
}

static IEnumerable<int> GetNumbers()
{
    var numbers = new int[] { 1, 2, 3 };
    foreach (int n in numbers)
    { 
        yield return n;
        Console.WriteLine($"回傳 {n} 之後");
    }
}

Enumerator.cs

IEnumerator<int> e = GetNumbers().GetEnumerator();
while (e.MoveNext())
{
    Console.WriteLine($"取得 {e.Current}");
}

// 底下是先前的寫法，一併列出來，方便對照。
IEnumerable<int> numbers = GetNumbers();
foreach (int n in numbers)
{
    Console.WriteLine($"取得 {n}");
}

GetNumbers-2.cs

IEnumerable<int> GetNumbers()
{
    yield return 1;
    Console.WriteLine("回傳 1 之後");
    yield return 2;
    Console.WriteLine("回傳 2 之後");
    yield return 3;
    Console.WriteLine("回傳 3 之後");
}

GetNumbers-3.cs

IEnumerable<int> GetNumbers()
{
    var numbers = await SomeApi.GetNumbersAsync();
    foreach (int n in numbers)
    { 
        yield return n;
        Console.WriteLine($"回傳 {n} 之後");
    }
}

GetNumbers-4.cs

async IEnumerable<int> GetNumbers()
{
    var numbers = await SomeApi.GetNumbersAsync();
    ... (略)
}

GetNumbers-5.cs

async IAsyncIEnumerable<int> GetNumbers()
{
    var numbers = await SomeApi.GetNumbersAsync();
    foreach (int n in numbers)
    { 
        yield return n;
        Console.WriteLine($"回傳 {n} 之後");
    }
}

GetNumbers-6.cs

IAsyncEnumerable<int> numbers = GetNumbers();
await foreach (int n in numbers)
{
    Console.WriteLine($"取得 {n}");
}

async IAsyncEnumerable<int> GetNumbers()
{
    await Task.Delay(1000);
    yield return 1;
    await Task.Delay(1000);
    yield return 2;
    await Task.Delay(1000);
    yield return 3;
}