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CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Runtime.CompilerServices;
					
public static class Program
{
	// Was having issues with the NuGet package so wrote a custom Range function instead, at the bottom
	
	public static async Task Main()
	{
		var sequence_A = Range("A{0}", 1, 5);  // note the DIFFERENT size ranges
		var sequence_B = Range("B{0}", 1, 3);
		var sequence_C = Range("C{0}", 1, 7);
		var merged = Interleave(sequence_A, sequence_B, sequence_C);
		await foreach (var item in merged) { Console.WriteLine(item); await Task.Delay(100); }
	}
	
	public static IAsyncEnumerable<T> Interleave<T>(params IAsyncEnumerable<T>[] sources) =>
		Interleave(default, sources);
	
	public static async IAsyncEnumerable<T> Interleave<T>([EnumeratorCancellation] CancellationToken token, IAsyncEnumerable<T>[] sources)
	{
		if(sources.Length == 0)
			yield break;
		var enumerators = new List<(IAsyncEnumerator<T> e, Task<bool> t)>(sources.Length);
		try
		{
			for(var i = 0; i < sources.Length; i++)
			{
				var e = sources[i].GetAsyncEnumerator(token);
				enumerators.Add((e, e.MoveNextAsync().AsTask()));
			}

			do
			{
				var taskResult = await Task.WhenAny(enumerators.Select(tuple => tuple.t));
				var ind = enumerators.FindIndex(tuple => tuple.t == taskResult);
				if(ind == -1) throw new Exception("ind was "+ind);
				var tuple = enumerators[ind];
				enumerators.RemoveAt(ind);
				if(taskResult.Result)
				{
					yield return tuple.e.Current;
					enumerators.Add((tuple.e, tuple.e.MoveNextAsync().AsTask()));
				}
				else
				{
					try
					{
						await tuple.e.DisposeAsync();
					}
					catch
					{ //
					}
				}
			} while (enumerators.Count > 0);
		}
		finally
		{
			for(var i = 0; i < enumerators.Count; i++)
			{
				try
				{
					await enumerators[i].e.DisposeAsync();
				}
				catch
				{ //
				}
			}
		}
	}
	
	static async IAsyncEnumerable<string> Range(string text, int start, int count) {
		for (int i = 0; i < count; i++)
		{
			var delayTask = Task.Delay(50);
			yield return string.Format(text, start + i);
			await delayTask;
		}
	}
}