Proxy Patterns Skill

Reference skill for proxy patterns in Solidity. Detailed proxy implementations are covered in the contract-patterns skill.

When to Use

Use this skill when:

• Implementing upgradeable contracts
• Choosing proxy pattern
• Understanding proxy mechanics
• Reviewing upgrade implementations

Related Skills

For detailed proxy implementations, see:

• contract-patterns: patterns/upgradeable-contracts.md
• upgrade-safety: Safe upgrade practices
• security-audit: checklists/upgrade-checklist.md

Proxy Pattern Overview

Pattern Comparison

UUPS (Universal Upgradeable Proxy Standard)

Recommended for most use cases

import "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";

contract MyContract is UUPSUpgradeable, OwnableUpgradeable {
    constructor() {
        _disableInitializers();
    }

    function initialize() public initializer {
        __Ownable_init(msg.sender);
        __UUPSUpgradeable_init();
    }

    function _authorizeUpgrade(address) internal override onlyOwner {}
}

Pros:

• Gas efficient
• Flexible upgrade authorization
• Smaller proxy contract

Cons:

• Can brick if _authorizeUpgrade removed
• More complex implementation

Detailed documentation: See contract-patterns/patterns/upgradeable-contracts.md

Transparent Proxy

Use when admin/user separation is critical

import "@openzeppelin/contracts/proxy/transparent/TransparentUpgradeableProxy.sol";

// Deploy
TransparentUpgradeableProxy proxy = new TransparentUpgradeableProxy(
    implementationAddress,
    adminAddress,
    initData
);

Pros:

• Clear admin/user separation
• Admin cannot call implementation functions
• Battle-tested pattern

Cons:

• Higher gas costs
• Larger proxy contract

Detailed documentation: See contract-patterns/patterns/upgradeable-contracts.md

Beacon Proxy

Use for multiple instances sharing implementation

import "@openzeppelin/contracts/proxy/beacon/UpgradeableBeacon.sol";
import "@openzeppelin/contracts/proxy/beacon/BeaconProxy.sol";

// Deploy beacon
UpgradeableBeacon beacon = new UpgradeableBeacon(implementationAddress);

// Deploy proxies
BeaconProxy proxy1 = new BeaconProxy(address(beacon), initData);
BeaconProxy proxy2 = new BeaconProxy(address(beacon), initData);

// Upgrade all
beacon.upgradeTo(newImplementation);

Pros:

• Upgrade multiple contracts at once
• Gas efficient for many instances
• Centralized control

Cons:

• All instances upgrade together
• Additional beacon contract

Detailed documentation: See contract-patterns/patterns/upgradeable-contracts.md

Diamond Pattern (EIP-2535)

Use for contracts exceeding size limits

Complex pattern with multiple facets. See EIP-2535 for specification.

Storage Layout Rules

Critical for all proxy patterns:

// V1
contract V1 {
    uint256 public value;
    address public owner;
}

// V2 - ✅ Safe upgrade
contract V2 {
    uint256 public value;      // Same position
    address public owner;      // Same position
    uint256 public newValue;   // Added at end
}

// V2 - ❌ Unsafe upgrade
contract V2Bad {
    address public owner;      // ❌ Changed position
    uint256 public value;      // ❌ Changed position
}

Rules:

1. Never delete state variables
2. Never change types
3. Never change order
4. Only add at the end
5. Use storage gaps in base contracts

Quick Pattern Selection

Choose UUPS if:

• You want gas efficiency
• You need flexible upgrade control
• You're comfortable with the pattern

Choose Transparent if:

• You need strict admin/user separation
• Gas cost is less critical
• You want simplicity

Choose Beacon if:

• Deploying many similar contracts
• Need to upgrade all together
• Want centralized upgrade control

Choose Diamond if:

• Contract exceeds 24KB limit
• Need modular functionality
• Comfortable with complexity

Related Documentation

• Implementation examples: contract-patterns/patterns/upgradeable-contracts.md
• Security checklist: security-audit/checklists/upgrade-checklist.md
• Upgrade safety: upgrade-safety/SKILL.md
• Example contract: contract-patterns/examples/upgradeable-example.sol

Note: This is a reference skill. For detailed implementations and examples, see the contract-patterns skill.