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ERC20.sol

View Source: openzeppelin-solidity/contracts/token/ERC20/ERC20.sol

↗ Extends: IERC20 ↘ Derived Contracts: SimpleToken

ERC20

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.
  • For a detailed writeup see our guide 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)

Arguments

Name Type Description

balanceOf

⤾ overrides IERC20.balanceOf

See IERC20.balanceOf.

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

Arguments

Name Type Description
account address

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

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

approve

⤾ overrides IERC20.approve

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

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

Arguments

Name Type Description
spender address
value uint256

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 value.
  • 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

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

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

_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

_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

_burn

Destoys 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 value) internal nonpayable

Arguments

Name Type Description
account address
value uint256

_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 value) internal nonpayable

Arguments

Name Type Description
owner address
spender address
value uint256

_burnFrom

Destoys 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

Contracts