# Modules on Endless Endless allows for permissionless publishing of modules within a package as well as upgrading those that have appropriate compatibility policy set. A module contains several structs and functions, much like Rust. During package publishing time, a few constraints are maintained: * Both Structs and public function signatures are published as immutable. * Only when a module is being published for the first time, and not during an upgrade, will the VM search for and execute an `init_module(account: &signer)` function. The signer of the account that is publishing the module is passed into the `init_module` function of the contract. **This function must be private and not return any value.** {% hint style="info" %} `init_module` is optional It is only necessary if you want to initialize data when publishing a module for the first time. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.endless.link/endless/devbuild/build/learn-the-move-language/advanced-move-guides/modules-on-endless.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.