@openzeppelin/contracts-upgradeable
Advanced tools
@openzeppelin/contracts-upgradeable is a library for secure smart contract development. It provides reusable and upgradeable smart contract components that follow best practices in security and gas efficiency. The package is particularly useful for creating upgradeable smart contracts, which can be modified after deployment without changing their address.
Upgradeable Contracts
This feature allows you to create upgradeable contracts using the Initializable base contract. The `initialize` function is used instead of a constructor to set initial values.
```json
{
"code": "import { Initializable } from '@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol';\n\ncontract MyContract is Initializable {\n uint256 public value;\n\n function initialize(uint256 _value) public initializer {\n value = _value;\n }\n}"}
```Access Control
This feature provides role-based access control mechanisms. The `AccessControlUpgradeable` contract allows you to define roles and restrict access to certain functions based on these roles.
```json
{
"code": "import { AccessControlUpgradeable } from '@openzeppelin/contracts-upgradeable/access/AccessControlUpgradeable.sol';\n\ncontract MyAccessControl is Initializable, AccessControlUpgradeable {\n bytes32 public constant ADMIN_ROLE = keccak256('ADMIN_ROLE');\n\n function initialize(address admin) public initializer {\n _setupRole(ADMIN_ROLE, admin);\n }\n}"}
```ERC20 Token
This feature allows you to create upgradeable ERC20 tokens. The `ERC20Upgradeable` contract provides the standard ERC20 functionality, and the `initialize` function sets the token's name and symbol.
```json
{
"code": "import { ERC20Upgradeable } from '@openzeppelin/contracts-upgradeable/token/ERC20/ERC20Upgradeable.sol';\n\ncontract MyToken is Initializable, ERC20Upgradeable {\n function initialize(string memory name, string memory symbol) public initializer {\n __ERC20_init(name, symbol);\n }\n}"}
```zos-lib is a library for writing upgradeable smart contracts. It provides similar functionalities to @openzeppelin/contracts-upgradeable, including initializable contracts and upgradeable proxies. However, it is less actively maintained compared to @openzeppelin/contracts-upgradeable.
Truffle is a development environment, testing framework, and asset pipeline for Ethereum. While it does not focus solely on upgradeable contracts, it provides tools for managing smart contract development and deployment, including migrations which can be used to handle upgrades.
Hardhat is a development environment for Ethereum software. It offers a flexible and extensible way to manage smart contract development and testing. While it does not provide built-in support for upgradeable contracts, it can be used in conjunction with other libraries like @openzeppelin/contracts-upgradeable to achieve similar functionality.
OpenZeppelin Contracts Upgradeable
This repository hosts the Upgradeable variant of OpenZeppelin Contracts, meant for use in upgradeable contracts. This variant is available as separate package called @openzeppelin/contracts-upgradeable.
It follows all of the rules for Writing Upgradeable Contracts: constructors are replaced by initializer functions, state variables are initialized in initializer functions, and we additionally check for storage incompatibilities across minor versions.
:warning: Warning
There will be storage incompatibilities across major versions of this package, which makes it unsafe to upgrade a deployed contract from one major version to another, for example from 3.4.0 to 4.0.0.
Similarly, it is not safe to upgrade from
@openzeppelin/contracts-ethereum-package(a similar previous package) to@openzeppelin/contracts-upgradeable.It is strongly encouraged to use these contracts together with a tool that can automatically guarantee the safety of an upgradeable contract, such as the OpenZeppelin Upgrades Plugins.
$ npm install @openzeppelin/contracts-upgradeable
The package replicates the structure of the main OpenZeppelin Contracts package, but every file and contract has the suffix Upgradeable.
-import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+import "@openzeppelin/contracts-upgradeable/token/ERC721/ERC721Upgradeable.sol";
-contract MyCollectible is ERC721 {
+contract MyCollectible is ERC721Upgradeable {
Constructors are replaced by internal initializer functions following the naming convention __{ContractName}_init. Since these are internal, you must always define your own public initializer function and call the parent initializer of the contract you extend.
- constructor() ERC721("MyCollectible", "MCO") {
+ function initialize() initializer public {
+ __ERC721_init("MyCollectible", "MCO");
}
Caution
Use with multiple inheritance requires special care. Initializer functions are not linearized by the compiler like constructors. Because of this, each
__{ContractName}_initfunction embeds the linearized calls to all parent initializers. As a consequence, calling two of theseinitfunctions can potentially initialize the same contract twice.The function
__{ContractName}_init_unchainedfound in every contract is the initializer function minus the calls to parent initializers, and can be used to avoid the double initialization problem, but doing this manually is not recommended. We hope to be able to implement safety checks for this in future versions of the Upgrades Plugins.
If you're new to smart contract development, head to Developing Smart Contracts to learn about creating a new project and compiling your contracts.
To keep your system secure, you should always use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
The guides in the docs site will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
The full API is also thoroughly documented, and serves as a great reference when developing your smart contract application. You can also ask for help or follow Contracts's development in the community forum.
Finally, you may want to take a look at the guides on our blog, which cover several common use cases and good practices.. The following articles provide great background reading, though please note, some of the referenced tools have changed as the tooling in the ecosystem continues to rapidly evolve.
This project is maintained by OpenZeppelin, and developed following our high standards for code quality and security. OpenZeppelin Contracts is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
The core development principles and strategies that OpenZeppelin Contracts is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
The latest audit was done on October 2018 on version 2.0.0.
Please report any security issues you find via our bug bounty program on Immunefi or directly to security@openzeppelin.org.
Critical bug fixes will be backported to past major releases.
OpenZeppelin Contracts exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the contribution guide!
OpenZeppelin Contracts is released under the MIT License.
4.4.2 (2022-01-11)
GovernorCompatibilityBravo: Fix error in the encoding of calldata for proposals submitted through the compatibility interface with explicit signatures. (#3100)FAQs
Secure Smart Contract library for Solidity
We found that @openzeppelin/contracts-upgradeable demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 4 open source maintainers collaborating on the project.
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