using System;

using System.Collections.Generic;

using System.Threading.Tasks;

using System.Linq;

​

public class Bar

{

}

​

public class Foo

{

}

​

public class ValidationResult

{

    public ValidationResult(string s)

    {

    }

}

​

public class Program

{

    private static async IAsyncEnumerable<int> ThisShouldReturnAsTask()

    {

        yield return 0;

        await Task.Delay(100);

        yield return 1;

    }

​

    private static IEnumerable<string> GetErrors(Bar bar, Foo foo)

    {

        yield return "Something is wrong";

        yield return "Oops something else is wrong";

        yield return "And eventually, this thing is wrong too";

    }

    private static Task<Foo> GetRequiredThingAsync()

    {

        return Task.FromResult(new Foo());

    }

    public async IAsyncEnumerable<ValidationResult> ValidateAsync1(Bar bar)

    {

        var foo = await GetRequiredThingAsync();

        foreach(var vr in GetErrors(bar, foo).Select(e => new ValidationResult(e))

        {

            yield return vr;

        }

    }

    public async Task<IAsyncEnumerable<ValidationResult>> ValidateAsync2(Bar bar)

    {

        var foo = await GetRequiredThingAsync();

        return GetErrors(bar, foo).Select(e => new ValidationResult(e)).ToAsyncEnumerable();

    }

​

    public async void Exercise()

    {

        await foreach(var f in ValidateAsync1(new Bar()))

        {

        }

        await foreach(var f in await ValidateAsync2(new Bar()))

        {

        }

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}