Writing Extensions

@jcoglan Not Rack extensions, but the API Sinatra provides to register modules. I have controller like extensions

The “Classic” style, where applications are defined on main / the top-level – most of the examples and documentation target this usage. Classic applications are often single-file, standalone apps that are run directly from the command line or with a minimal rackup file. When an extension is required in a classic application, the expectation is that all extension functionality should be present without additional setup on the application developers part (like included/extending modules). The “Modular” style, where Sinatra::Base is subclassed explicitly and the application is defined within the subclass’s scope. These applications are often bundled as libraries and used as components within a larger Rack-based system. Modular applications must include any desired extensions explicitly by calling register ExtensionModule within the application’s class scope.

Full article: http://www.sinatrarb.com/extensions.html