FlipTheSwitch

A feature switching/toggling/flipping library for ObjectiveC.

flip_the_switch

A gem command line tool for generating the Features.plist & FTSFlipTheSwitch+Features.{h,m} categories to help with the corresponding Pod.

The Problem

We have a a new feature we've been working on, AmazingFeature, and we've been building it inside a branch. Now has come the time to finally merge it back in. This then takes us the next day, as the MyApp.xcodeproj/project.pbxproj file has a lot of conflicting changes, and we get things wrong a lot before we get them right. We weren't able to rebase often, as multiple people were working on this branch, and so we also had to keep regularly merging in all of the other changes from the rest of the team, constantly losing focus of our goal. We finally have it all merged and then... everything breaks!

The way to avoid all of these constant merges/rebases/context switches is to always have our code in the master branch, but we didn't want to affect the rest of the team while they released QuickerFeature in the next release cycle.

How can we get the benefits of working on master branch, while still not worrying about breaking the other features while we build AmazingFeature?

Introducing FlipTheSwitch

Auto-Generated Files:

With 'FTSFlipTheSwitch', we can choose different code paths at runtime:

self.newFeatureButton.hidden = [[FTSFlipTheSwitch sharedInstance] isFeatureEnabled:@"new_feature"];

The features can be enabled/disabled at runtime:

[[FTSFlipTheSwitch sharedInstance] enableFeature:@"new_feature"];

[[FTSFlipTheSwitch sharedInstance] disableFeature:@"new_feature"];

[[FTSFlipTheSwitch sharedInstance] setFeature:@"new_feature" enabled:YES];

All enabled features will persist between app loads through NSUserDefaults.

The features can defaulted to enabled/disabled via a plist file Features.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>disabled_feature</key>
    <dict>
        <key>description</key>
        <string>is disabled description</string>
        <key>enabled</key>
        <false/>
    </dict>
    <key>enabled_feature</key>
    <dict>
        <key>enabled</key>
        <true/>
    </dict>
</dict>
</plist>

Subfeatures

You can add as many subfeatures to a feature recursively. Resulting in a plist as e.g. :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>description</key>
        <string>is disabled description</string>
        <key>enabled</key>
        <false/>
        <key>subfeature</key>
        <dict>
            <key>enabled</key>
            <true/>
        </dict>
    </dict>
</plist>

Configuration Screen

• shows all features, their description texts and enabled state
• easily switching features on and off
• reset all feature back to the original setting from the plist (based on the json)

Notifications

When a feature status changes, you can find out about it by listening for the notification titled FTSFeatureStatusChangedNotification, which contains:

• FTSFeatureStatusChangedNotificationFeatureKey - the key of the feature being enabled/disabled
• FTSFeatureStatusChangedNotificationEnabledKey - the NSNumber of whether the feature was enabled or disabled

Plattform Support

• iOS
  • example project
  • full test coverage
  • configuration screen
• Mac OSX
  • example project
  • full test coverage

Command-Line-Interface

If you install the gem, you will be able to use the Command-Line-Interface.

The CLI consists of 3 commands:

• plist - creates a Features.plist file for enabled/disabled features including their description (optional) like that mentioned above.
• settings - creates a Settings.bundle used by the OS settings. These can then be used to enable/disable the features at runtime.
• category - creates FTSFlipTheSwitch+Features.{h,m} files for features, thus giving compile-time checks for adding/removal of new features. e.g:

/* AUTO-GENERATED. DO NOT ALTER */
#import <FlipTheSwitch/FTSFlipTheSwitch.h>

@interface FTSFlipTheSwitch (Features)

+ (BOOL)isAwesomeFeatureEnabled;
+ (void)enableAwesomeFeature;
+ (void)disableAwesomeFeature;
+ (void)setAwesomeFeatureEnabled:(BOOL)enabled;
+ (void)resetAwesomeFeatureController;
+ (NSString *)awesomeFeatureControllerKey;

@end

Define Features and subfeatures

The features and subfeatures, along with their default enabled/disabled state, are read from a features.json file. e.g.:

{
    "default": {
        "awesome_feature": {
            "enabled": true,    
            "description": "Makes this project awesome",
            "sub_feature": {
                "enabled": true,
                "description": "Makes this project even more awesome"       
            }
        }
    },
    "beta": {
        "inherits_from": "default",
        "awesome_feature": {
            "enabled": false
        }
    }
}    

In order to avoid typing in the same options all the time, you can create a .flip.yml file for the default options, e.g.:

input: features
environment: development
category_output: Classes/Extensions

For more information, run flip-the-switch help

How to install

Add pod 'FlipTheSwitch' to your Podfile

Add gem 'flip_the_switch' to your Gemfile

Authors

• Michael England @ SoundCloud
• Rob Siwek @ SoundCloud
• Kristina Roddewig @ SoundCloud
• Vincent Garrigues @ SoundCloud

License

FlipTheSwitch is available under the MIT license. See the LICENSE file for more info.