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Extensões de tokens

Pausable e Burnable

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Extending Tokens

The base ERC-20 only handles transfers and approvals. OpenZeppelin provides extensions that add features by inheritance:

Pausable — freeze transfers in emergencies.
Burnable — let holders destroy tokens.
Capped — enforce a maximum supply.
Permit — gasless approvals via signatures.

Combining via Inheritance

You mix extensions by listing multiple base contracts:

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";

contract MyToken is ERC20, ERC20Burnable {
    constructor() ERC20("MyToken", "MTK") {}
}

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";

contract MyToken is ERC20, ERC20Burnable {
    constructor() ERC20("MyToken", "MTK") {}
}

Burnable Tokens

ERC20Burnable adds two functions:

burn(amount) — destroys the caller's own tokens.
burnFrom(account, amount) — burns from an account that approved you.

Burning reduces totalSupply, which can be used for deflationary mechanics.

// holder destroys their tokens
token.burn(ethers.parseEther("100"));

Pausable Tokens

ERC20Pausable lets an authorized account halt all transfers — useful during a security incident:

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Pausable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, ERC20Pausable, Ownable {
    function pause() public onlyOwner { _pause(); }
    function unpause() public onlyOwner { _unpause(); }
}

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Pausable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, ERC20Pausable, Ownable {
    function pause() public onlyOwner { _pause(); }
    function unpause() public onlyOwner { _unpause(); }
}

How Pause Works

When paused, transfers revert with EnforcedPause. The Pausable extension hooks into the token's internal transfer logic, so transfer, transferFrom, mint, and burn are all blocked until unpause is called.

Use pausing sparingly — it centralizes control.

Resolving Function Conflicts

When two parents define the same internal hook, Solidity requires you to override it and specify the order:

function _update(address from, address to, uint256 value)
    internal override(ERC20, ERC20Pausable) {
    super._update(from, to, value);
}

This tells the compiler how to linearize the inheritance.

function _update(address from, address to, uint256 value)
    internal override(ERC20, ERC20Pausable) {
    super._update(from, to, value);
}

Capped Supply

ERC20Capped enforces a hard maximum supply set at deployment:

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";

contract MyToken is ERC20Capped {
    constructor()
        ERC20("MyToken", "MTK")
        ERC20Capped(1000000 * 10 ** 18) {}
}

Any mint that would exceed the cap reverts.

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";

contract MyToken is ERC20Capped {
    constructor()
        ERC20("MyToken", "MTK")
        ERC20Capped(1000000 * 10 ** 18) {}
}

Gasless Approvals with Permit

ERC20Permit lets users approve spending with an off-chain signature instead of an on-chain approve transaction:

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";

contract MyToken is ERC20, ERC20Permit {
    constructor()
        ERC20("MyToken", "MTK")
        ERC20Permit("MyToken") {}
}

This improves UX by removing one transaction.

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";

contract MyToken is ERC20, ERC20Permit {
    constructor()
        ERC20("MyToken", "MTK")
        ERC20Permit("MyToken") {}
}

Extensions for NFTs Too

ERC-721 has parallel extensions:

ERC721Enumerable — iterate over all tokens.
ERC721URIStorage — per-token metadata URIs.
ERC721Burnable / ERC721Pausable — same ideas as ERC-20.

The pattern of composing through inheritance is the same.

Compose Only What You Need

Each extension adds code, gas cost, and surface area. Include only the features your token actually requires:

Fewer extensions mean cheaper deployment and a smaller attack surface.
Document why each extension is present.

Votes Extension

ERC20Votes tracks historical voting power by snapshotting balances at each block, enabling on-chain governance:

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";

Holders can delegate their votes, and proposals can query past voting power to prevent flash-loan manipulation.

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";

Quick Check

Test your understanding of token extensions.

Recap

You learned to compose token features with extensions.

Extensions add behavior by multiple inheritance.
Burnable destroys tokens; Capped enforces max supply.
Pausable freezes transfers in emergencies.
Permit enables gasless, signature-based approvals.
Resolve hook conflicts by overriding (e.g. _update) and include only what you need.

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