Swevo.AutoFeatureFlag 1.0.1

Swevo.AutoFeatureFlag

Compile-time feature flag stubs for .NET. Decorate an enum with [FeatureFlags] and get a strongly-typed interface and class — no reflection, no Microsoft.FeatureManagement overhead, AOT-safe.

[FeatureFlags]
public enum AppFeatures
{
    DarkMode,
    NewCheckout,
    BetaApi
}

// ↓ Generator produces ↓

public interface IAppFeaturesFlags
{
    bool IsDarkModeEnabled   { get; }
    bool IsNewCheckoutEnabled { get; }
    bool IsBetaApiEnabled    { get; }
}

public sealed class AppFeaturesFlags : IAppFeaturesFlags
{
    public AppFeaturesFlags(IFeatureFlagProvider provider) ...
    public bool IsDarkModeEnabled    => provider.IsEnabled("DarkMode");
    public bool IsNewCheckoutEnabled => provider.IsEnabled("NewCheckout");
    public bool IsBetaApiEnabled     => provider.IsEnabled("BetaApi");
}

Why not Microsoft.FeatureManagement?

Quick Start

dotnet add package Swevo.AutoFeatureFlag

// 1. Define your flags
[FeatureFlags]
public enum Features { DarkMode, BetaCheckout }

// 2. Wire up (choose your DI framework)
var provider = new InMemoryFeatureFlagProvider();
services.AddSingleton<IFeatureFlagProvider>(provider);
services.AddSingleton<IFeaturesFlags, FeaturesFlags>();

// 3. Inject and use
public class CheckoutService(IFeaturesFlags flags)
{
    public void Process()
    {
        if (flags.IsBetaCheckoutEnabled)
            RunBetaCheckout();
        else
            RunCheckout();
    }
}

InMemoryFeatureFlagProvider

The bundled in-memory provider is thread-safe and defaults all flags to disabled.

var provider = new InMemoryFeatureFlagProvider();

provider.Enable("DarkMode");           // → IsEnabled("DarkMode") == true
provider.Disable("DarkMode");          // → IsEnabled("DarkMode") == false
provider.SetEnabled("DarkMode", true); // same as Enable

Testing

public class CheckoutServiceTests
{
    private readonly InMemoryFeatureFlagProvider _provider = new();
    private readonly FeaturesFlags _flags;

    public CheckoutServiceTests() => _flags = new FeaturesFlags(_provider);

    [Fact]
    public void BetaCheckout_WhenEnabled_UsesBetaPath()
    {
        _provider.Enable("BetaCheckout");
        var sut = new CheckoutService(_flags);
        // assert beta path taken ...
    }
}

Custom Providers

Implement IFeatureFlagProvider to read from any source — configuration, database, LaunchDarkly, etc.:

public sealed class ConfigFeatureFlagProvider(IConfiguration config) : IFeatureFlagProvider
{
    public bool IsEnabled(string flagName)
        => config.GetValue<bool>($"FeatureFlags:{flagName}");

    public void Enable(string flagName)  => throw new NotSupportedException("Use appsettings.json");
    public void Disable(string flagName) => throw new NotSupportedException("Use appsettings.json");
    public void SetEnabled(string flagName, bool enabled) => throw new NotSupportedException();
}

Diagnostics

Part of the Swevo ecosystem

License

MIT © 2026 Justin Bannister