# OpenZeppelin Contracts v3.0 final release candidate

**URL:** <https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583>\
**Category:** Announcements\
**Created:** [April 3, 2020, 9:01pm UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583 "2020-04-03T21:01:49Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![nventuro](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/nventuro/32/8_2.png) [@nventuro](https://forum.openzeppelin.com/u/nventuro)\
**Post date:** [April 3, 2020, 9:01pm UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/1 "2020-04-03T21:01:49Z")

</div>

![a847d600e1565ea24f914b4c29b224160376602d](https://us1.discourse-cdn.com/flex022/uploads/zeppelin/original/2X/4/4cc3a2ecb186c925df99e94f38ec2bee6c073cee.png)

We’re excited to announce the last **release candidate of OpenZeppelin Contracts v3.0** ✨

This means we’re **close the v3.0 final release** , the main goal in our [Q1 roadmap](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2068). Stay tuned for our upcoming plans for the next quarter!

Among other things, this release features the **migration to Solidity v0.6** , as well as a **revamped access control system** , **streamlined token contracts** , and new libraries for **enumerable mappings**.

To install the release candidate, run:

```bash
npm install --save-dev @openzeppelin/contracts@next

```

## What’s New

- All contracts were migrated to Solidity v0.6.
- `AccessControl` was designed [with help from the community](https://forum.openzeppelin.com/t/redesigning-accesscontrol-for-the-openzeppelin-contracts/2177) and has replaced `Roles` contracts (such as `MinterRole` and `PauserRole`), which were removed.
- Crowdsales were removed: we’ll continue to provide support for security issues on the v2.5 release, but will not bring them over to v3.0.
- We’ve added **hooks** , a new feature of the library that will make extending it easier than ever. Read more below!
- `ERC20` and `ERC721` were simplified and streamlined, including all optional parts of the standard by default, and simplifying some of our own custom extensions.
- Support for better `mapping` types that let you efficiently iterate over all keys using `EnumerableSet` and `EnumerableMap`
- Many, _many_ breaking changes with small improvements. We’ve also moved some contracts around (e.g. `Ownable` is now found under the `access` directory) and deleted some that were not being used. Head to our [changelog](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CHANGELOG.md) to see the full list.

## Compiling v0.6 Contracts

You can use the [**OpenZeppelin CLI**](https://docs.openzeppelin.com/cli) to compile any Solidity v0.6 contract: just update the `pragma` statement on your source code and you’ll be good to go!

```auto
pragma solidity ^0.6.0;

```

Note that you will need to use the [recent v2.7 release of the CLI](https://forum.openzeppelin.com/t/openzeppelin-cli-2-7/2252) to have Solidity v0.6 support. For detailed information about using the CLI compiler, head to its [documenation](https://docs.openzeppelin.com/cli/compiling).

## Revamped Access Control

One of our most widely-used contracts is [`Ownable`](https://docs.openzeppelin.com/contracts/2.x/api/ownership#Ownable), providing a simple authorization scheme. However, this fell short in complex systems with [multiple permissions](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/366).

The v3.0 release introduces `AccessControl`, a one-stop-shop for all authorization needs. It lets you easily define multiple **roles with different permissions** , as well as **which accounts are allowed to grant and revoke** each role. It also boosts transparency by enabling **enumeration of all privileged accounts** in a system.

`AccessControl` was designed with a security-first mindset, [receiving input from a wide array of users](https://forum.openzeppelin.com/t/redesigning-accesscontrol-for-the-openzeppelin-contracts/2177) and incorporating best practices in the field. Head to [our Access Control guide](https://docs.openzeppelin.com/contracts/3.x-rc/access-control#role-based-access-control) for more information!

## Deploy Ready Contracts

OpenZeppelin Contracts shine when as a library to develop custom smart contracts, but that’s not all they can do! We’ve added **Deploy Ready** variants for ERC20 and ERC721 tokens: contracts you can deploy as-is to get your tokens out there quickly **without having to write any Solidity code**. Check out [their documentation!](https://docs.openzeppelin.com/contracts/3.x-rc/api/deploy-ready)

## Migrating From OpenZeppelin Contracts v2.5

Other than the contract removals mentioned above, the library API is pretty much the same as in the [v2.5 release](https://forum.openzeppelin.com/t/openzeppelin-contracts-v2-5/2155), so the migration should be straightforward. For instructions on how to update your Solidity v0.5 contracts to v0.6, refer to the [official documentation](https://solidity.readthedocs.io/en/v0.6.2/060-breaking-changes.html#how-to-update-your-code).

If you’re using the `ERC20` or `ERC721` tokens however, you’ll have to remove all references to optional extensions (`ERC20Detailed`, `ERC721Enumerable`, etc.) - these have been included in the base contracts.

The other exception to this are contracts that use the [**Gas Station Network (GSN)**](https://docs.openzeppelin.com/contracts/2.x/gsn): if you’re inheriting from `GSNRecipient` or one of the other GSN contracts, you’ll need to add the following snippet to your contracts:

```auto
function _msgSender() internal view override(Context, GSNRecipient) returns (address payable) {
    return GSNRecipient._msgSender();
}

function _msgData() internal view override(Context, GSNRecipient) returns (bytes memory) {
    return GSNRecipient._msgData();
}

```

## Using Hooks

To improve library flexibility, we’re introducing **hooks** : functions that are called at specific moments during a contract’s operation that you can use to _hook_ into the internals and extend as you wish.

For example, the `_beforeTokenTransfer` hook in ERC20, ERC721 and ERC777 makes it very easy to add additional checks or actions to execute whenever tokens are transferred, minted or burned, regardless of what prompted it.

```bash
// Tokens can only be transferred, minted or burned if the contract is not paused
contract ERC20Pausable is ERC20, Pausable {
    function _beforeTokenTransfer(address from, address to, uint256 amount) 
        internal virtual override 
    {
        super._beforeTokenTransfer(from, to, amount);

        require(!paused(), "ERC20Pausable: token transfer while paused");
    }
}

```

As an additional benefit, using hooks will allow you to side-step some of the [edge-cases product of the new `override` keyword](https://github.com/ethereum/solidity/issues/8141).

## Next Steps

As with all release candidates, the final release will follow one or two weeks later. This is so that community members get a chance to share their thoughts on the upcoming changes before they are made final.

So give this release candidate a try, upgrade your project to Solidity v0.6, and tell us what you think!

---

<div class="post-metadata">

**Author:** ![abcoathup](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/abcoathup/32/415_2.png) [@abcoathup](https://forum.openzeppelin.com/u/abcoathup)\
**Post date:** [April 6, 2020, 10:24am UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/2 "2020-04-06T10:24:42Z")

</div>

Awesome work @nventuro 🙏

# ERC721

Is `tokenUri` going to be made `virtual` in 3.0 [https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2154](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/2154) ?

This would allow automatic token URI [https://github.com/OpenZeppelin/openzeppelin-contracts/issues/1745](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/1745)

# Deploy Ready ERC721

It would be great to have a deploy ready ERC721 that includes meta data (with automatic token URI [https://github.com/OpenZeppelin/openzeppelin-contracts/issues/1745](https://github.com/OpenZeppelin/openzeppelin-contracts/issues/1745)).

I would ❤ to hear from the community on what they would like to see in a deploy ready ERC721.

Something like the following:

## MyERC721

```auto
pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/access/AccessControl.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

contract MyERC721 is Context, AccessControl, ERC721 {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant BASEURI_SETTER_ROLE = keccak256(
        "BASEURI_SETTER_ROLE"
    );

    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor(string memory name, string memory symbol, string memory baseURI) public ERC721(name, symbol) {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        _setupRole(BASEURI_SETTER_ROLE, _msgSender());

        _setBaseURI(baseURI);
    }

    function mint(address to) public {
        require(
            hasRole(MINTER_ROLE, msg.sender),
            "MyERC721: account does not have minter role"
        );
        _tokenIds.increment();

        uint256 newTokenId = _tokenIds.current();
        _mint(to, newTokenId);
    }

    function tokenURI(uint256 tokenId) public view override returns (string memory) {
        require(_exists(tokenId), "MyERC721: URI query for nonexistent token");

        return string(abi.encodePacked(baseURI(), Strings.fromUint256(tokenId)));
    }

    function setBaseURI(string memory baseURI) public {
        require(
            hasRole(BASEURI_SETTER_ROLE, msg.sender),
            "MyERC721: account does not have setter role"
        );
        _setBaseURI(baseURI);
    }
}

```

# Deploy Ready Fixed Supply ERC20

Should there also be a simple ERC20 with a fixed supply in Deploy Ready?  
Equivalent of SimpleToken in Contracts 2.5: [https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v2.5.0/contracts/examples/SimpleToken.sol](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v2.5.0/contracts/examples/SimpleToken.sol)

---

<div class="post-metadata">

**Author:** ![Chxpz](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/chxpz/32/2068_2.png) [@Chxpz](https://forum.openzeppelin.com/u/Chxpz)\
**Post date:** [April 10, 2020, 5:18am UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/3 "2020-04-10T05:18:58Z")

</div>

Hi mate.  
Any reason why the crowdsale contract was removed?

Are there intentions to replace it by any other similar contract?

Thank you.

---

<div class="post-metadata">

**Author:** ![abcoathup](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/abcoathup/32/415_2.png) [@abcoathup](https://forum.openzeppelin.com/u/abcoathup)\
**Post date:** [April 10, 2020, 7:58am UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/4 "2020-04-10T07:58:43Z")

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Hi @Chxpz,

Welcome to the community 👋

Please see the documentation on why Crowdsales were removed:  
[https://docs.openzeppelin.com/contracts/3.x-rc/crowdsales](https://docs.openzeppelin.com/contracts/3.x-rc/crowdsales)

---

<div class="post-metadata">

**Author:** ![k06a](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/k06a/32/60_2.png) [@k06a](https://forum.openzeppelin.com/u/k06a)\
**Post date:** [April 11, 2020, 12:44pm UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/5 "2020-04-11T12:44:09Z")

</div>

Solidity 0.6.0 became more explicit on functions overriding, requires specification linearity of multiple inheritance. This broken everything.

---

<div class="post-metadata">

**Author:** ![julianmrodri](https://avatars.discourse-cdn.com/v4/letter/j/8edcca/32.png) [@julianmrodri](https://forum.openzeppelin.com/u/julianmrodri)\
**Post date:** [April 11, 2020, 12:45pm UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/6 "2020-04-11T12:45:11Z")

</div>

Hi team! I also noticed the Pausable contract is not available anymore in this new release. I have to implement a Pausable smart contract in 0.6 which path do you suggest to follow? Thanks!

---

<div class="post-metadata">

**Author:** ![nventuro](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/nventuro/32/8_2.png) [@nventuro](https://forum.openzeppelin.com/u/nventuro)\
**Post date:** [April 20, 2020, 7:20pm UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/8 "2020-04-20T19:20:59Z")

</div>

`Pausable` is still available: it was [moved into the `utils` directory](https://docs.openzeppelin.com/contracts/3.x-rc/api/utils#Pausable).

---

<div class="post-metadata">

**Author:** ![abcoathup](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/abcoathup/32/415_2.png) [@abcoathup](https://forum.openzeppelin.com/u/abcoathup)\
**Post date:** [April 21, 2020, 2:15am UTC](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0-final-release-candidate/2583/9 "2020-04-21T02:15:31Z")

</div>

OpenZeppelin Contracts v3.0 is released ✨

> [@OpenZeppelin Contracts v3.0](https://forum.openzeppelin.com/t/openzeppelin-contracts-v3-0/2695):
>
> We’re thrilled to finally announce the release of OpenZeppelin Contracts v3.0 sparkles Among other things, this release features the migration to Solidity v0.6, as well as a revamped access control system, streamlined token contracts, and new libraries for enumerable mappings. To install this latest release, run: npm install --save-dev @openzeppelin/contracts What’s New All contracts were migrated to Solidity v0.6. AccessControl was designed [w…](https://forum.openzeppelin.com/t/redesigning-accesscontrol-for-the-openzeppelin-contracts/2177)