Control Flow: Loops, foreach with IEnumerable & IAsyncEnumerable Streaming

1Concept

foreach iterates over any type implementing IEnumerable or with a GetEnumerator() method. C# 8+ introduced IAsyncEnumerable<T> and await foreach for asynchronous streaming of database rows or Kafka messages without buffering entire collections in memory.

2Architecture Diagram

await foreach (var item in FetchAsyncStream()) ──► Yields items as they arrive over network!

3Code Example

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

class Program
{
    // Asynchronous Streaming Generator
    static async IAsyncEnumerable<string> FetchStockUpdatesAsync()
    {
        string[] stocks = ["AAPL: $185", "MSFT: $420", "NVDA: $120"];
        foreach (var s in stocks)
        {
            await Task.Delay(50); // Simulate network latency
            yield return s;
        }
    }

    static async Task Main()
    {
        Console.WriteLine("=== Consuming IAsyncEnumerable Stream ===");
        await foreach (var update in FetchStockUpdatesAsync())
        {
            Console.WriteLine($"Live Ticker: {update}");
        }
    }
}

4Expected Output

=== Consuming IAsyncEnumerable Stream ===
Live Ticker: AAPL: $185
Live Ticker: MSFT: $420
Live Ticker: NVDA: $120

5Key Takeaways

• ✓Use IAsyncEnumerable<T> with yield return for real-time streaming APIs.
• ✓foreach over List<T> uses a struct enumerator that allocates zero heap garbage.
• ✓LINQ queries are lazily evaluated until enumerated by foreach or .ToList().