> For the complete documentation index, see [llms.txt](https://docs.endless.link/endless/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.endless.link/endless/devbuild/build/learn-the-move-language/advanced-move-guides/modules-on-endless.md).

# 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 %}


---

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