From feature models to feature toggles in practice

Feature Toggles (often also referred to as Feature Flags) are a powerful technique, providing an alternative to maintaining multiple feature branches in source code. A condition within the code enables or disables a feature at runtime, hence providing a kind of runtime variability resolution. Several works have already identified the proximity of this concept with the notion of Feature found in Software Product Lines. In this paper, we propose to go one step further in unifying these concepts to provide a seamless transition between design time and runtime variability resolutions. We propose to model all the variability using a feature model. Then this feature model can be partially resolved at design time (yielding an incomplete product derivation), the unresolved variability being used to generate feature toggles that can be enabled/disabled at runtime. We first demonstrate these ideas on the toy example of the Expression Product Line , and then show how it can scale to build a configurable authentication system, where a partially resolved feature model can interface with popular feature toggle frameworks such as Togglz.