.. index:: storage

Storage Patterns

.. _simple_storage:

.. warning::

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

Let's start with a minimal contract that demonstrates state storage. This contract stores a single integer that can be set by anyone.

Simple Storage

.. literalinclude:: ../../examples/storage/storage.vy :language: vyper :linenos:

This example shows:

A public state variable storedData with an auto-generated getter
A constructor (__init__) that sets the initial value
An external function set() that modifies state

The public modifier on storedData automatically creates a getter function, so external contracts can read the value by calling contract.storedData().

.. index:: storage;advanced

.. _advanced_storage:

Advanced Storage

Building on the simple storage example, this contract adds input validation, events, and a reset function.

.. literalinclude:: ../../examples/storage/advanced_storage.vy :language: vyper :linenos:

New concepts introduced:

Events: The DataChange event logs who changed the value and what they changed it to. The indexed keyword allows filtering by the setter's address.
Assertions with messages: assert _x >= 0, "No negative values" reverts with a readable error.
Business logic guards: The contract locks when the stored value reaches 100.