ERC20.sol
View Source: home/circleci/project/node_modules/@openzeppelin/contracts/token/ERC20/ERC20.sol
โ Extends: Context, IERC20 โ 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}.
Contract Members
Constants & Variables
Functions
- constructor
- name
- symbol
- decimals
- totalSupply
- balanceOf
- transfer
- allowance
- approve
- transferFrom
- increaseAllowance
- decreaseAllowance
- _transfer
- _mint
- _burn
- _approve
- _setupDecimals
- _beforeTokenTransfer
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.
Arguments
Name | Type | Description |
---|---|---|
name_ | string | |
symbol_ | string |
name
Returns the name of the token.
Arguments
Name | Type | Description |
---|
symbol
Returns the symbol of the token, usually a shorter version of the name.
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}.
Arguments
Name | Type | Description |
---|
totalSupply
See {IERC20-totalSupply}.
Arguments
Name | Type | Description |
---|
balanceOf
See {IERC20-balanceOf}.
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
.
Arguments
Name | Type | Description |
---|---|---|
recipient | address | |
amount | uint256 |
allowance
See {IERC20-allowance}.
Arguments
Name | Type | Description |
---|---|---|
owner | address | |
spender | address |
approve
See {IERC20-approve}. Requirements:
spender
cannot be the zero address.
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
andrecipient
cannot be the zero address.sender
must have a balance of at leastamount
.- the caller must have allowance for
sender
's tokens of at leastamount
.
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.
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 leastsubtractedValue
.
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 leastamount
.
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.
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 leastamount
tokens.
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.
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.
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
andto
are both non-zero,amount
offrom
's tokens will be to transferred toto
. - when
from
is zero,amount
tokens will be minted forto
. - when
to
is zero,amount
offrom
's tokens will be burned. from
andto
are never both zero. To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
Arguments
Name | Type | Description |
---|---|---|
from | address | |
to | address | |
amount | uint256 |