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* Added documentation for Feature Toggle design pattern * Explanation for Feature Toggle Issue #2230 finished, added intent, explanation, programmatic example, applicability and consequences
87 lines
3.8 KiB
Markdown
87 lines
3.8 KiB
Markdown
---
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title: Feature Toggle
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category: Behavioral
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language: en
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tag:
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- Extensibility
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---
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## Also known as
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Feature Flag
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## Intent
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A technique used in software development to control and manage the rollout of specific features or functionality in a
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program without changing the code. It can act as an on/off switch for features depending on the status or properties of
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other values in the program. This is similar to A/B testing, where features are rolled out based on properties such as
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location or device. Implementing this design pattern can increase code complexity, and it is important to remember to
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remove redundant code if this design pattern is being used to phase out a system or feature.
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## Explanation
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Real-world Example
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> This design pattern works really well in any sort of development, in particular mobile development. Say you want to
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> introduce a feature such as dark mode, but you want to ensure that the feature works correctly and don't want to roll
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> out the feature to everyone immediately. You write in the code, and have it switched off as default. From here, it is
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> easy to turn on the code for specific users based on selection criteria, or randomly. This will also allow the feature
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> to be turned off easily without any drastic changes to the code, or any need for redeployment or updates.
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In plain words
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> Feature Toggle is a way to introduce new features gradually instead of deployment all at once.
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Wikipedia says
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> A feature toggle in software development provides an alternative to maintaining multiple feature branches in source
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> code. A condition within the code enables or disables a feature during runtime. In agile settings the toggle is
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> used in production, to switch on the feature on demand, for some or all the users.
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## Programmatic Example
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This example shows Java code that allows a feature to show when it is enabled by the developer, and when a user is a
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Premium member of the application. This is useful for subscription locked features.
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```java
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public class FeatureToggleExample {
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// Bool for feature enabled or disabled
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private static boolean isNewFeatureEnabled = false;
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public static void main(String[] args) {
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boolean userIsPremium = true; // Example: Check if the user is a premium user
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// Check if the new feature should be enabled for the user
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if (userIsPremium && isNewFeatureEnabled) {
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// User is premium and the new feature is enabled
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showNewFeature();
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}
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}
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private static void showNewFeature() {
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// If user is allowed to see locked feature, this is where the code would go
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}
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}
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```
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The code shows how simple it is to implement this design pattern, and the criteria can be further refined or broadened
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should the developers choose to do so.
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## Class diagram
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## Applicability
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Use the Feature Toggle pattern when
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* Giving different features to different users.
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* Rolling out a new feature incrementally.
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* Switching between development and production environments.
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* Quickly disable problematic features
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* External management of feature deployment
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* Ability to maintain multiple version releases of a feature
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* 'Hidden' deployment, releasing a feature in code for designated testing but not publicly making it available
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## Consequences
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Consequences involved with using the Feature Toggle pattern
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* Code complexity is increased
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* Testing of multiple states is harder and more time-consuming
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* Confusion between friends on why features are missing
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* Keeping documentation up to date with all features can be difficult
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## Credits
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* [Martin Fowler 29 October 2010 (2010-10-29).](http://martinfowler.com/bliki/FeatureToggle.html)
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* [Feature Toggle - Java Design Patterns](https://java-design-patterns.com/patterns/feature-toggle/)
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