@sotolf iirc C uses a preprocessor, it isn't part of the language itself. Most dynamic languages do not support conditional compilation because they aren't compiled. I literally meant the `--feature` command line flag for cargo which is one of the ways to use `#cfg` to affect Rust's conditional compilation. In my daily language, the general term "feature flag" only affects runtime behavior, like disabling a still in development new feature of a web app or service. Not the same thing here.