Skip to content

Latest commit

 

History

History
721 lines (598 loc) · 20.9 KB

ERC20.md

File metadata and controls

721 lines (598 loc) · 20.9 KB
Raw

ERC20.sol

View Source: contracts/openzeppelin/ERC20.sol

↗ Extends: Context, IERC20_ ↘ Derived Contracts: SOV

ERC20 contract

Implementation of the {IERC20} interface.

  • This implementation is agnostic to the way tokens are created. This means that a supply mechanism has to be added in a derived contract using {_mint}. For a generic mechanism see {ERC20Mintable}.
  • TIP: For a detailed writeup see our guide https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How to implement supply mechanisms].
  • We have followed general OpenZeppelin guidelines: functions revert instead of returning false on failure. This behavior is nonetheless conventional and does not conflict with the expectations of ERC20 applications.
  • Additionally, an {Approval} event is emitted on calls to {transferFrom}. This allows applications to reconstruct the allowance for all accounts just by listening to said events. Other implementations of the EIP may not emit these events, as it isn't required by the specification.
  • Finally, the non-standard {decreaseAllowance} and {increaseAllowance} functions have been added to mitigate the well-known issues around setting allowances. See {IERC20-approve}.

Contract Members

Constants & Variables

mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;

Functions

totalSupply

⤾ overrides IERC20_.totalSupply

See {IERC20-totalSupply}.

function totalSupply() public view
returns(uint256)
Source Code 
function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

balanceOf

⤾ overrides IERC20_.balanceOf

See {IERC20-balanceOf}.

function balanceOf(address account) public view
returns(uint256)

Arguments

Name Type Description
account address
Source Code 
function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

transfer

⤾ overrides IERC20_.transfer

See {IERC20-transfer}. * Requirements: * - recipient cannot be the zero address.

  • the caller must have a balance of at least amount.
function transfer(address recipient, uint256 amount) public nonpayable
returns(bool)

Arguments

Name Type Description
recipient address
amount uint256
Source Code 
function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

allowance

⤾ overrides IERC20_.allowance

See {IERC20-allowance}.

function allowance(address owner, address spender) public view
returns(uint256)

Arguments

Name Type Description
owner address
spender address
Source Code 
function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }

approve

⤾ overrides IERC20_.approve

See {IERC20-approve}. * Requirements: * - spender cannot be the zero address.

function approve(address spender, uint256 amount) public nonpayable
returns(bool)

Arguments

Name Type Description
spender address
amount uint256
Source Code 
function approve(address spender, uint256 amount) public returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

transferFrom

⤾ overrides IERC20_.transferFrom

See {IERC20-transferFrom}. * Emits an {Approval} event indicating the updated allowance. This is not required by the EIP. See the note at the beginning of {ERC20}; * Requirements:

  • sender and recipient cannot be the zero address.
  • sender must have a balance of at least amount.
  • the caller must have allowance for sender's tokens of at least amount.
function transferFrom(address sender, address recipient, uint256 amount) public nonpayable
returns(bool)

Arguments

Name Type Description
sender address
recipient address
amount uint256
Source Code 
function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            _msgSender(),
            _allowances[sender][_msgSender()].sub(
                amount,
                "ERC20: transfer amount exceeds allowance"
            )
        );
        return true;
    }

increaseAllowance

Atomically increases the allowance granted to spender by the caller. * This is an alternative to {approve} that can be used as a mitigation for problems described in {IERC20-approve}. * Emits an {Approval} event indicating the updated allowance. * Requirements: * - spender cannot be the zero address.

function increaseAllowance(address spender, uint256 addedValue) public nonpayable
returns(bool)

Arguments

Name Type Description
spender address
addedValue uint256
Source Code 
function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

decreaseAllowance

Atomically decreases the allowance granted to spender by the caller. * This is an alternative to {approve} that can be used as a mitigation for problems described in {IERC20-approve}. * Emits an {Approval} event indicating the updated allowance. * Requirements: * - spender cannot be the zero address.

  • spender must have allowance for the caller of at least subtractedValue.
function decreaseAllowance(address spender, uint256 subtractedValue) public nonpayable
returns(bool)

Arguments

Name Type Description
spender address
subtractedValue uint256
Source Code 
function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(
            _msgSender(),
            spender,
            _allowances[_msgSender()][spender].sub(
                subtractedValue,
                "ERC20: decreased allowance below zero"
            )
        );
        return true;
    }

_transfer

Moves tokens amount from sender to recipient. * This is internal function is equivalent to {transfer}, and can be used to e.g. implement automatic token fees, slashing mechanisms, etc. * Emits a {Transfer} event. * Requirements: * - sender cannot be the zero address.

  • recipient cannot be the zero address.
  • sender must have a balance of at least amount.
function _transfer(address sender, address recipient, uint256 amount) internal nonpayable

Arguments

Name Type Description
sender address
recipient address
amount uint256
Source Code 
function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(
            amount,
            "ERC20: transfer amount exceeds balance"
        );
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

_mint

Creates amount tokens and assigns them to account, increasing the total supply. * Emits a {Transfer} event with from set to the zero address. * Requirements * - to cannot be the zero address.

function _mint(address account, uint256 amount) internal nonpayable

Arguments

Name Type Description
account address
amount uint256
Source Code 
function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

_burn

Destroys amount tokens from account, reducing the total supply. * Emits a {Transfer} event with to set to the zero address. * Requirements * - account cannot be the zero address.

  • account must have at least amount tokens.
function _burn(address account, uint256 amount) internal nonpayable

Arguments

Name Type Description
account address
amount uint256
Source Code 
function _burn(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

_approve

Sets amount as the allowance of spender over the owners tokens. * This is internal function is equivalent to approve, and can be used to e.g. set automatic allowances for certain subsystems, etc. * Emits an {Approval} event. * Requirements: * - owner cannot be the zero address.

  • spender cannot be the zero address.
function _approve(address owner, address spender, uint256 amount) internal nonpayable

Arguments

Name Type Description
owner address
spender address
amount uint256
Source Code 
function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

_burnFrom

Destroys amount tokens from account.amount is then deducted from the caller's allowance. * See {_burn} and {_approve}.

function _burnFrom(address account, uint256 amount) internal nonpayable

Arguments

Name Type Description
account address
amount uint256
Source Code 
function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(
            account,
            _msgSender(),
            _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance")
        );
    }

Contracts