Explaining complex algorithms or logic

There may be times where you need to explain complex algorithms or logic in your code. This can be challenging, especially when you're trying to make it understandable to others. Copilot Chat can help you with this task by providing you with suggestions on how to explain the algorithm or logic in a clear and concise manner.

Example scenario

In the C# code below, we have a method which fetches data, retries if there's an error, and updates a status label. You might want to explain, in comments in the code, how the method works and how it handles retries and cancellations.

private static readonly HttpClient _client = new HttpClient();

public async Task<string> FetchDataFromApiWithRetryAsync(string apiUrl, CancellationToken cancellationToken, int maxRetries, int cancellationDelay, Label statusLabel)
{
    var retryCount = 0;
    using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

    while (retryCount < maxRetries)
    {
        try
        {
            cts.CancelAfter(cancellationDelay);
            return await FetchDataFromApiAsync(cts.Token, statusLabel);
        }
        catch (Exception ex) when (!(ex is OperationCanceledException))
        {
            if (retryCount < maxRetries - 1) {
                retryCount++;
                int delay = (int)Math.Pow(2, retryCount) * 1000;
                await Task.Delay(delay, cancellationToken);
                UpdateStatusLabel($"Retrying ({retryCount}/{maxRetries})...", statusLabel);
            } else {
                throw new Exception($"Failed to fetch data after {maxRetries} retries: {ex.Message}", ex);
            }
        }
    }

    throw new OperationCanceledException("The operation was cancelled.", cts.Token);
}

private async Task<string> FetchDataFromApiAsync(string apiUrl, CancellationToken cancellationToken, Label statusLabel)
{
    UpdateStatusLabel("Fetching data...", statusLabel);

    HttpResponseMessage response = await _client.GetAsync(apiUrl, cancellationToken);
    response.EnsureSuccessStatusCode();
    string data = await response.Content.ReadAsStringAsync();

    UpdateStatusLabel("Data fetched.", statusLabel);
    return data;
}

private void UpdateStatusLabel(string message, Label statusLabel)
{
    if (statusLabel.InvokeRequired) {
        statusLabel.BeginInvoke(new Action<string, Label>(UpdateStatusLabel), message, statusLabel);
    } else {
        statusLabel.Text = message;
    }
}

Example prompt

We can ask Copilot Chat to make this code easier to understand using comments.

Add comments to this code to make it more understandable

Example response

Copilot responds with an overview of the update it suggests, and the code snippet with the comments added:

// Shared HttpClient instance for making HTTP requests (best practice for reuse)
private static readonly HttpClient _client = new HttpClient();

/// <summary>
/// Fetches data from an API with retry mechanism and timeout functionality
/// </summary>
/// <param name="apiUrl">The URL to fetch data from</param>
/// <param name="cancellationToken">Token to cancel the operation</param>
/// <param name="maxRetries">Maximum number of retry attempts</param>
/// <param name="cancellationDelay">Timeout duration in milliseconds</param>
/// <param name="statusLabel">UI label to show status updates</param>
public async Task<string> FetchDataFromApiWithRetryAsync(string apiUrl, CancellationToken cancellationToken, int maxRetries, int cancellationDelay, Label statusLabel)
{
    var retryCount = 0;
    // Create a linked cancellation token that combines user cancellation and timeout
    using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

    while (retryCount < maxRetries)
    {
        try
        {
            // Set timeout for this attempt
            cts.CancelAfter(cancellationDelay);
            return await FetchDataFromApiAsync(cts.Token, statusLabel);
        }
        catch (Exception ex) when (!(ex is OperationCanceledException))
        {
            // If not the last retry attempt, implement exponential backoff
            if (retryCount < maxRetries - 1) {
                retryCount++;
                // Exponential backoff: 2^retryCount seconds (1s, 2s, 4s, 8s, etc.)
                int delay = (int)Math.Pow(2, retryCount) * 1000;
                await Task.Delay(delay, cancellationToken);
                UpdateStatusLabel($"Retrying ({retryCount}/{maxRetries})...", statusLabel);
            } else {
                // If all retries failed, throw exception with details
                throw new Exception($"Failed to fetch data after {maxRetries} retries: {ex.Message}", ex);
            }
        }
    }

    // This is reached if maxRetries is 0 or some other unexpected case
    throw new OperationCanceledException("The operation was cancelled.", cts.Token);
}

/// <summary>
/// Makes the actual API call to fetch data
/// </summary>
private async Task<string> FetchDataFromApiAsync(string apiUrl, CancellationToken cancellationToken, Label statusLabel)
{
    UpdateStatusLabel("Fetching data...", statusLabel);

    // Perform HTTP GET request with cancellation support
    HttpResponseMessage response = await _client.GetAsync(apiUrl, cancellationToken);
    response.EnsureSuccessStatusCode(); // Throws if response is not successful
    string data = await response.Content.ReadAsStringAsync();

    UpdateStatusLabel("Data fetched.", statusLabel);
    return data;
}

/// <summary>
/// Updates UI label text safely across threads
/// </summary>
/// <param name="message">The message to display</param>
/// <param name="statusLabel">The label control to update</param>
private void UpdateStatusLabel(string message, Label statusLabel)
{
    // Check if we need to invoke on UI thread
    if (statusLabel.InvokeRequired) {
        // Use BeginInvoke to update label on UI thread
        statusLabel.BeginInvoke(new Action<string, Label>(UpdateStatusLabel), message, statusLabel);
    } else {
        // Direct update if already on UI thread
        statusLabel.Text = message;
    }
}

Further reading

• "GitHub Copilot のプロンプト エンジニアリング"
• "GitHub Copilot の使用についてのベスト プラクティス"