ERC20.sol

View Source: home/circleci/project/node_modules/@openzeppelin/contracts/token/ERC20/ERC20.sol

↗ Extends: Context, IERC20 ↘ Derived Contracts: Token

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 {ERC20PresetMinterPauser}. 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}.

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Contract Members

Constants & Variables

mapping(address => uint256) private _balances;

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

uint256 private _totalSupply;

string private _name;

string private _symbol;

uint8 private _decimals;

Functions

• constructor
• name
• symbol
• decimals
• totalSupply
• balanceOf
• transfer
• allowance
• approve
• transferFrom
• increaseAllowance
• decreaseAllowance
• _transfer
• _mint
• _burn
• _approve
• _setupDecimals
• _beforeTokenTransfer

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constructor

Sets the values for {name} and {symbol}, initializes {decimals} with a default value of 18. To select a different value for {decimals}, use {_setupDecimals}. All three of these values are immutable: they can only be set once during construction.

constructor(string name_, string symbol_) public nonpayable

Arguments

Name	Type	Description
name_	string
symbol_	string

name

Returns the name of the token.

function name() public view

returns(string)

Arguments

Name	Type	Description

symbol

Returns the symbol of the token, usually a shorter version of the name.

function symbol() public view

returns(string)

Arguments

Name	Type	Description

decimals

Returns the number of decimals used to get its user representation. For example, if decimals equals 2, a balance of 505 tokens should be displayed to a user as 5,05 (505 / 10 ** 2). Tokens usually opt for a value of 18, imitating the relationship between Ether and Wei. This is the value {ERC20} uses, unless {setupDecimals} is called. NOTE: This information is only used for _display purposes: it in no way affects any of the arithmetic of the contract, including {IERC20-balanceOf} and {IERC20-transfer}.

function decimals() public view

returns(uint8)

Arguments

Name	Type	Description

totalSupply

See {IERC20-totalSupply}.

function totalSupply() public view

returns(uint256)

Arguments

Name	Type	Description

balanceOf

See {IERC20-balanceOf}.

function balanceOf(address account) public view

returns(uint256)

Arguments

Name	Type	Description
account	address

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

See {IERC20-allowance}.

function allowance(address owner, address spender) public view

returns(uint256)

Arguments

Name	Type	Description
owner	address
spender	address

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

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

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

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

_approve

Sets amount as the allowance of spender over the owner s tokens. This 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

_setupDecimals

Sets {decimals} to a value other than the default one of 18. WARNING: This function should only be called from the constructor. Most applications that interact with token contracts will not expect {decimals} to ever change, and may work incorrectly if it does.

function _setupDecimals(uint8 decimals_) internal nonpayable

Arguments

Name	Type	Description
decimals_	uint8

_beforeTokenTransfer

Hook that is called before any transfer of tokens. This includes minting and burning. Calling conditions:

• when from and to are both non-zero, amount of from's tokens will be to transferred to to.
• when from is zero, amount tokens will be minted for to.
• when to is zero, amount of from's tokens will be burned.
• from and to are never both zero. To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].

function _beforeTokenTransfer(address from, address to, uint256 amount) internal nonpayable

Arguments

Name	Type	Description
from	address
to	address
amount	uint256