# Bootstrap pattern

**🟢 Beginner · Lesson 18**

The composition root - ONE function that binds the whole world and hands back the conduit. Configured things are BUILT there and bound as instances; everything else in the app just melds. Note: melder worlds do not "switch environments" - the same objects cannot register twice (a spell_id is the SHA256 of an object's code and data), so your MODULE decides what to build, once, at the root.

## Before you run

Use the [Beginner guide](../../beginner/index.md) for prerequisite concepts. Run from a checkout with Melder installed and Python 3.14 free-threading selected. The collection download includes the level's local helper modules.

## Run the saved script

```bash
python UX_and_AIX_experiences/01_beginner/18_bootstrap_pattern.py
```

```powershell
py -3.14t UX_and_AIX_experiences/01_beginner/18_bootstrap_pattern.py
```

{download}`Download this collection <../../downloads/beginner-examples.zip>` · [Source on GitHub](https://github.com/Synaptic724/melder/blob/90d52e0a12cb0743d62568d5a19ce954a54443bc/UX_and_AIX_experiences/01_beginner/18_bootstrap_pattern.py)

## Public surface

the build_world() pattern, instance spells

## Code

```{literalinclude} ../../downloads/01_beginner/18_bootstrap_pattern.py
:language: python
:linenos:
```

## Check the outcome

The script contains its own assertions or demonstrated refusal paths. Run it to evaluate those checks against your installed version. The code above is taken directly from the saved file; no run output is invented here.

[More beginner examples](index.md) · [Level guide](../../beginner/index.md)

## Related guides

- [Build a complete beginner application](../../beginner/capstone.md)