static async IAsyncEnumerable<User> GetUsersAsync(int delayMilliseconds = 500)
    for (int page = 1; page <= 3; page++)
        await Task.Delay(delayMilliseconds);
        var users = new List<User>
            new User((page - 1) * 3 + 1, "Alice"),
            new User((page - 1) * 3 + 2, "Bob"),
            new User((page - 1) * 3 + 3, "John")
        foreach (var user in users)
            yield return user;
When it comes to converting IAsyncEnumerable<T> to List<T>, the built-in ToListAsync() method from the System.Linq.Async NuGet package offers a powerful and suitable option. It’s also worth noting that this method is different from the EntityFrameworkQueryableExtensions ToListAsync(IQueryable<T>) method.
Let’s see how to use it to convert our sample GetUserAsync() method:
static async Task<List<User>> GetUsersAsListAsync(int delayMilliseconds = 500)
    var usersAsync = GetUsersAsync(delayMilliseconds);
    return await usersAsync.ToListAsync();
Here, we can see that the conversion process is incredibly concise. By invoking ToListAsync() on an IAsyncEnumerable<T> instance and awaiting the result, we obtain a readily available List<T>.
To validate the output and confirm that it indeed returns a List<T>, we can utilize the built-in GetType() method:
var usersAsync = GetUsersAsync();
var usersList = await usersAsync.ToListAsync();
Console.WriteLine(usersList.GetType());
Using GetType(), we retrieve the underlying type of our userList variable and then write it to the console:

System.Collections.Generic.List`1[ConvertIAsyncEnumerableToListLibrary.Model.User]
Our output indicates that the conversion has resulted in a List<T> collection, as expected.
Using ToListAsync() Method With Cancellation Token for Conversion

While the ToListAsync() method is simple and convenient for conversion, it is important to be aware of its possible drawbacks, particularly when dealing with potentially long-running asynchronous operations.
How conversion using this method works is that it buffers the entire dataset into memory before returning the List<T>. When working with huge datasets, this can result in memory exhaustion or performance bottlenecks, especially if the procedure takes longer than expected.
This is where the need to use a cancellation token comes in, acting as a sort of safeguard for our asynchronous operations. By providing a CancellationToken to the ToListAsync() method, we can cancel the data retrieval and processing if necessary.
To use the cancellation token in our method, we first have to modify our IAsyncEnumerable method GetUsersAsync() to respect the provided token. This is a great practice that ensures the operation can be canceled efficiently at any point during its execution:
static async IAsyncEnumerable<User> GetUsersAsync
(int delayMilliseconds = 500, [EnumeratorCancellation] CancellationToken cancellationToken = default)
    for (int page = 1; page <= 3; page++)
        await Task.Delay(delayMilliseconds, cancellationToken);
        var users = new List<User>
            new User((page - 1) * 3 + 1, "Alice"),
            new User((page - 1) * 3 + 2, "Bob"),
            new User((page - 1) * 3 + 3, "John")
        foreach (var user in users)
            cancellationToken.ThrowIfCancellationRequested();
            yield return user;
In this modified version, we pass the CancellationToken to Task.Delay to allow the delay to be cancelable. Additionally, we call cancellationToken.ThrowIfCancellationRequested() before yielding each user, to ensure that the operation can be canceled at any point.
With the CancellationToken now integrated into our GetUsersAsync() method, we also need to adjust the GetUsersAsListAsync() method to support cancellation:

static async Task<List<User>> GetUsersAsListAsync
(int delayMilliseconds = 500, CancellationToken cancellationToken = default)
    var usersAsync = GetUsersAsync(delayMilliseconds, cancellationToken);
    return await usersAsync.ToListAsync(cancellationToken);
In our code, we pass the CancellationToken to both the GetUsersAsync() and ToListAsync() methods. This setup ensures that if a cancellation is requested, it can be propagated through both the asynchronous enumeration and the conversion to a list, allowing the operation to be canceled at any point.
Check out our article for a detailed explanation of utilizing CancellationToken for asynchronous operations.
Conclusion

Throughout this article, we’ve looked at how to convert IAsyncEnumerable to a List in C#, delving into the reasoning behind it and the practical method for doing so. We also talked about the advantage of employing a cancellation token during this conversion.
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