.. index:: factory pattern

Factory Pattern

---

.. _factory:

.. warning::

This is example code for learning purposes. Do not use in production without thorough review and testing.

The factory pattern deploys and registers multiple contract instances. This example shows a factory that registers exchanges and routes trades between them.

Factory Contract

.. literalinclude:: ../../examples/factory/Factory.vy :language: vyper :linenos:

Exchange Contract

.. literalinclude:: ../../examples/factory/Exchange.vy :language: vyper :linenos:

How the pattern works:

1. Deploy the Exchange code and record its codehash
2. Deploy the Factory with the exchange codehash
3. Deploy Exchange instances (one per token)
4. Each Exchange calls factory.register() to register itself
5. The Factory verifies the caller's codehash matches the expected exchange code
6. Users can now trade between any registered tokens via factory.trade()

The msg.sender.codehash check ensures only legitimate exchange contracts can register.