#FeatureFlipper

A feature flipping system.

Feature flipping enable you to integrate your code earlier, avoiding feature branching. It can also be used to provide specific behaviour to specific users (A/B testing, beta-test users). http://martinfowler.com/bliki/FeatureToggle.html

Example of use:

    if(Features.Flipper.IsOn("feature1")) 
    {
        // do the job
    }

#How to use:

###1. Download NuGet package https://www.nuget.org/packages/FeatureFlipper

###2. Define some features

In your configuration file :

	...
	<appSettings>
		<add key="FeatureFlipper.Sample.FeatureByType" value="true" /> 
		<add key="featureByKey" value="true" />
		<add key="featureByDate" value="2000-01-01T00:00:00+00:00" />
	</appSettings>
	...
	

###3. Add code that is conditional on feature availability

    // By type feature flipping
    if (Features.Flipper.IsOn<FeatureByType>())
    {
        // do feature enabled by type ...
    }

    // By key feature flipping
    if (Features.Flipper.IsOn("featureByKey"))
    {
        // do feature enabled by key ...
    }

    // By date feature flipping
    if (Features.Flipper.IsOn("featureByDate"))
    {
        // do feature enabled by date
    }
	

#Go further

FeatureFlipper offer many extensibility points:

##Create your custom IFeatureProvider

A IFeatureProvider simply said "Hey ! I know this feature and it is ON (or OFF) !".

By default, FeatureFlipper provides ConfigurationFeatureProvider and RoleFeatureProvider.

See Extending the features provider for more details.

##Create your custom IConfigurationReader

The IConfigurationReader interface is used by the ConfigurationFeatureProvider. It provides the value of a feature given a feature key.

The default implementation reads the value into the app/web.config file, in the AppSettings section. You could create your own implementation by reading values from a SQL/NoSQL database, a web service or anything else.

See Extending the configuration reading for more details.

##Create your custom IFeatureStateParser The IFeatureStateParser interface is used by the ConfigurationFeatureProvider. It provides a boolean value for a feature given a feature state. The defaults implementations converts boolean strings to boolean values ("true" ==> ON; "false" ==> OFF). It can also convert dates representing string to boolean values, based on the predicate that past date means feature ON, an future date means feature OFF.

See Extending the configuration parsing for more details.

##Ioc via Unity The NuGet package FeatureFlipper.Unity wire FeatureFlipper with Unity. Feature flipping became much more easier with IoC :

In your configuration file :

	...
	<appSettings>
		<add key="FeatureFlipper.Unity.Sample.EmailSender" value="true" /> 
	</appSettings>
	...
	

In your Ioc configuration :

    // Add the Feature flipping extensions
    container.AddFeatureFlippingExtension();
	

In your code :

    
    // Get an object from the IoC container. 
    // This could be done anywhere in your code, for example by service location, constructor injection or property injection.
    IMessageSender sender = container.Resolve<IMessageSender>();
    
    ...

    // Call the code. Does not worry with 'if' statement.
    sender.SendMessage("This message is sent only if the feature is enabled.");
	

It is unnecessary to add a 'if' statement. When the feature is enabled, the Ioc container returns the desired object an its method is called. When the feature is disabled, the Ioc container returns a NullObject. Any method called on this object does nothing. It is a bit similar to the ConditionalAttribute.

#License & Copyright

This software is released under the MIT Licence. It is Copyright 2014, Yann Crumeyrolle. I may be contacted at [email protected].