Writes an .app file.

An .app file is a file containing Erlang terms that defines your application. Mix automatically generates this file based on your mix.exs configuration. You can learn more about OTP applications by seeing the documentation for the Application module.

In order to generate the .app file, Mix expects your application to have both :app and :version keys. Furthermore, you can configure the generated application by defining an application function in your mix.exs with the following options:

• :applications - all applications your application depends on at runtime. For example, if your application depends on Erlang’s :crypto, it needs to be added to this list. Most of your dependencies must be added as well (unless they’re a development or test dependency). Mix and other tools use this list in order to properly boot your application dependencies before starting the application itself.

• :registered - the name of all registered processes in the application. If your application defines a local GenServer with name MyServer, it is recommended to add MyServer to this list. It is mostly useful to detect conflicts between applications that register the same names.

• :mod - specify a module to invoke when the application is started, it must be in the format {Mod, args} where args is often an empty list. The module specified here must implement the callbacks defined by the Application module.

• :env - default values for the application environment. The application environment is one of the most common ways to configure applications.

Let’s see an example application function:

def application do
  [mod: {MyApp, []},
   env: [default: :value],
   applications: [:crypto]]
end

Besides the options above, .app files also expects other options like :modules and :vsn, but those are automatically filled by Mix.

Command line options

• --force - forces compilation regardless of modification times