A toggle switch can be found in various technology devices and applications that allow you to change the state of a feature such as WiFi(r) or Bluetooth(r). In software development a toggle is used to enable or disable features, switch between different display modes or otherwise manage the behavior of an application.
Often times a toggle is accompanied by some form of dynamic re-configuration such as a server side event trigger or a user interface button click. In this way a toggle provides an easy means of managing the state of an application without having to make major changes to code or introduce new features. This flexibility is one of the primary benefits of using toggles.
A word of caution, though: if not properly managed a toggle configuration can become a tangled mess. As more and more toggles are introduced and deployed they may impact each other in ways you hadn’t anticipated, creating complex conditional logic that can be difficult to read. In addition, if you don’t remove old toggles that have run their course, they can continue to impact the codebase long after they have been deemed unnecessary.
Toggle configuration can be managed in a number of ways ranging from static files where commenting is used to modify the toggle state through to more sophisticated approaches which are often based on a preprocessor’s #ifdef feature and offer much more dynamic re-configuration capabilities. Most organizations will use a combination of these techniques, implementing a centralized toggle configuration store alongside some type of admin UI which enables product managers, engineers and testers to view and modify feature flags and their configuration.
Whether your team chooses to deploy toggles through dynamic re-configuration or through some other method, they should be proactive in keeping their inventory as low as possible. This is best accomplished through a rigorous process for vetting feature toggles and ensuring they are appropriate to solve a given problem. Additionally, teams should be proactive in removing toggles that have run their course, adding code cleanup tasks to the backlog or building this process into their management platform.
It is important to test the toggle configuration that will be live in production, testing the toggle with its normal On state and also performing tests with the toggle flipped Off. Many organizations will also opt to include some additional tests with all toggles flipped On so they can see how any future releases might impact current and existing functionality. This approach reduces the amount of time that a team will spend debugging and helps to ensure quality in production. Regardless of how they are implemented, it is critical that each toggle has clear and visible labels and updates its appearance (typically by changing the background) when its state changes. This will help people understand the purpose and effect of the toggle in your application. It should also be easy for users to select the desired toggle state. This will also help to reduce cognitive overload.
