> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Storage

> Namespaced storage layout utilities for smart contracts

Utilities for calculating collision-resistant storage slots in upgradeable and modular smart contracts.

<Tip title="ERC References">
  Implements [ERC-7201](https://eips.ethereum.org/EIPS/eip-7201) (Namespaced Storage Layout) and [ERC-8042](https://eips.ethereum.org/EIPS/eip-8042) (Diamond Storage).
</Tip>

## Overview

Storage collisions are a critical issue in upgradeable proxies, libraries, and diamond patterns. When multiple contracts or versions share storage, overlapping slots cause data corruption.

ERC-7201 and ERC-8042 solve this by deterministically calculating storage slots from namespace identifiers, ensuring each module has isolated storage regions.

## Quick Start

<Tabs>
  <Tab title="ERC-7201 (Recommended)">
    ```typescript theme={null}
    import * as Storage from '@tevm/voltaire/Storage';
    import { keccak256 } from '@tevm/voltaire/crypto';

    // Calculate namespaced storage slot
    const slot = Storage.calculateErc7201(
      keccak256,
      'my.contract.storage'
    );

    // Use in contract storage layout
    // contract MyContract {
    //   struct MyStorage {
    //     uint256 value;
    //     mapping(address => uint256) balances;
    //   }
    //
    //   function getStorage() internal pure returns (MyStorage storage $) {
    //     assembly {
    //       $.slot := 0x... // <- Use calculated slot here
    //     }
    //   }
    // }
    ```
  </Tab>

  <Tab title="ERC-8042 (Diamond Storage)">
    ```typescript theme={null}
    import * as Storage from '@tevm/voltaire/Storage';
    import { keccak256 } from '@tevm/voltaire/crypto';

    // Calculate diamond storage slot
    const slot = Storage.calculateErc8042(
      keccak256,
      'diamond.standard.storage'
    );

    // Simpler formula: just keccak256(id)
    // Used by EIP-2535 Diamond Standard
    ```
  </Tab>
</Tabs>

## When to Use Each Standard

**ERC-7201** (Namespaced Storage Layout):

* General purpose upgradeable contracts
* UUPS proxies
* Transparent proxies
* Modular contract architectures
* Extra collision resistance (last byte cleared)

**ERC-8042** (Diamond Storage):

* EIP-2535 Diamond Standard contracts
* Multi-facet proxy patterns
* Legacy diamond implementations
* Simpler formula when compatibility required

## API Documentation

<CardGroup cols={2}>
  <Card title="calculateErc7201" icon="hashtag" href="/primitives/storage/calculate-erc7201">
    Calculate ERC-7201 namespaced storage slot
  </Card>

  <Card title="calculateErc8042" icon="gem" href="/primitives/storage/calculate-erc8042">
    Calculate ERC-8042 diamond storage slot
  </Card>
</CardGroup>

## Storage Collision Prevention

### Without Namespaced Storage

```solidity theme={null}
// ❌ DANGEROUS: Storage collision risk
contract ProxyV1 {
  uint256 value;        // slot 0
  address owner;        // slot 1
}

contract ProxyV2 {
  address newOwner;     // slot 0 - COLLISION!
  uint256 value;        // slot 1 - COLLISION!
}
```

### With ERC-7201

```solidity theme={null}
// ✅ SAFE: Isolated namespaced storage
contract ProxyV1 {
  struct V1Storage {
    uint256 value;
    address owner;
  }

  function getStorage() internal pure returns (V1Storage storage $) {
    assembly {
      $.slot := 0xabcd... // ERC-7201 slot
    }
  }
}

contract ProxyV2 {
  struct V2Storage {
    address newOwner;
    uint256 value;
  }

  function getStorage() internal pure returns (V2Storage storage $) {
    assembly {
      $.slot := 0x1234... // Different ERC-7201 slot
    }
  }
}
```

## Specification References

* [ERC-7201](https://eips.ethereum.org/EIPS/eip-7201) - Namespaced Storage Layout
* [ERC-8042](https://eips.ethereum.org/EIPS/eip-8042) - Diamond Storage (EIP-2535)
* [EIP-1967](https://eips.ethereum.org/EIPS/eip-1967) - Proxy Storage Slots
* [EIP-2535](https://eips.ethereum.org/EIPS/eip-2535) - Diamond Standard

## Related

* [Storage (Effect)](https://voltaire-effect.tevm.sh/primitives/storage) - Effect.ts integration with Schema validation
* [Proxy](/primitives/proxy) - Proxy patterns using namespaced storage
* [Keccak256](/crypto/keccak256) - Hash function for slot calculation
* [Bytes](/primitives/bytes) - Storage slot byte manipulation