How to Use Feature Flags in Rust Applications

Rust uses feature flags to enable unstable features in nightly builds, not as a runtime mechanism for toggling application logic. To use an unstable feature, add a #![feature(...)] attribute at the crate root and compile with the nightly toolchain.

#![feature(unstable_feature_name)]

fn main() {
    // Code using the unstable feature
}

For runtime feature toggling (e.g., enabling/disabling UI elements), use a third-party crate like feature-flags or config with environment variables, as Rust's built-in feature flags are compile-time only.

Feature flags in Rust are switches you flip before compiling your code to turn on experimental or unstable features. They are not meant for changing how your app behaves while it is running. Think of them like a factory setting that decides which parts of the engine are installed before the car leaves the lot.