IERC20
Interface of the ERC20 standard as defined in the EIP.
Functions
totalSupply()
balanceOf(account)
transfer(recipient, amount)
allowance(owner, spender)
approve(spender, amount)
transferFrom(sender, recipient, amount)
Events
Transfer(from, to, value)
Approval(owner, spender, value)
totalSupply() → uint256 external
Returns the amount of tokens in existence.
balanceOf(address account) → uint256 external
Returns the amount of tokens owned by account.
transfer(address recipient, uint256 amount) → bool external
Moves amount tokens from the caller’s account to recipient.
Returns a boolean value indicating whether the operation succeeded.
Emits a Transfer event.
allowance(address owner, address spender) → uint256 external
Returns the remaining number of tokens that spender will beallowed to spend on behalf of owner through transferFrom. This iszero by default.
This value changes when approve or transferFrom are called.
approve(address spender, uint256 amount) → bool external
Sets amount as the allowance of spender over the caller’s tokens.
Returns a boolean value indicating whether the operation succeeded.
| Beware that changing an allowance with this method brings the riskthat someone may use both the old and the new allowance by unfortunatetransaction ordering. One possible solution to mitigate this racecondition is to first reduce the spender’s allowance to 0 and set thedesired value afterwards:https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 |
Emits an Approval event.
transferFrom(address sender, address recipient, uint256 amount) → bool external
Moves amount tokens from sender to recipient using theallowance mechanism. amount is then deducted from the caller’sallowance.
Returns a boolean value indicating whether the operation succeeded.
Emits a Transfer event.
Transfer(address from, address to, uint256 value) event
Emitted when value tokens are moved from one account (from) toanother (to).
Note that value may be zero.
Approval(address owner, address spender, uint256 value) event
Emitted when the allowance of a spender for an owner is set bya call to approve. value is the new allowance.
ERC20
Implementation of the IERC20 interface.
This implementation is agnostic to the way tokens are created. This meansthat a supply mechanism has to be added in a derived contract using _mint.For a generic mechanism see ERC20PresetMinterPauser.
| For a detailed writeup see our guideHowto implement supply mechanisms. |
We have followed general OpenZeppelin guidelines: functions revert insteadof returning false on failure. This behavior is nonetheless conventionaland 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 justby listening to said events. Other implementations of the EIP may not emitthese events, as it isn’t required by the specification.
Finally, the non-standard decreaseAllowance and increaseAllowancefunctions have been added to mitigate the well-known issues around settingallowances. See IERC20.approve.
Functions
constructor(name_, symbol_)
name()
symbol()
decimals()
totalSupply()
balanceOf(account)
transfer(recipient, amount)
allowance(owner, spender)
approve(spender, amount)
transferFrom(sender, recipient, amount)
increaseAllowance(spender, addedValue)
decreaseAllowance(spender, subtractedValue)
_transfer(sender, recipient, amount)
_mint(account, amount)
_burn(account, amount)
_approve(owner, spender, amount)
_setupDecimals(decimals_)
_beforeTokenTransfer(from, to, amount)
Events
IERC20
Transfer(from, to, value)
Approval(owner, spender, value)
constructor(string name_, string symbol_) public
Sets the values for name and symbol, initializes decimals witha 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 duringconstruction.
name() → string public
Returns the name of the token.
symbol() → string public
Returns the symbol of the token, usually a shorter version of thename.
decimals() → uint8 public
Returns the number of decimals used to get its user representation.For example, if decimals equals 2, a balance of 505 tokens shouldbe displayed to a user as 5,05 (505 / 10 ** 2).
Tokens usually opt for a value of 18, imitating the relationship betweenEther and Wei. This is the value ERC20 uses, unless _setupDecimals iscalled.
| This information is only used for display purposes: it inno way affects any of the arithmetic of the contract, includingIERC20.balanceOf and IERC20.Transfer. |
totalSupply() → uint256 public
See IERC20.totalSupply.
balanceOf(address account) → uint256 public
See IERC20.balanceOf.
transfer(address recipient, uint256 amount) → bool public
See IERC20.Transfer.
Requirements:
recipientcannot be the zero address.the caller must have a balance of at least
amount.
allowance(address owner, address spender) → uint256 public
See IERC20.allowance.
approve(address spender, uint256 amount) → bool public
See IERC20.approve.
Requirements:
spendercannot be the zero address.
transferFrom(address sender, address recipient, uint256 amount) → bool public
See IERC20.transferFrom.
Emits an Approval event indicating the updated allowance. This is notrequired by the EIP. See the note at the beginning of ERC20.
Requirements:
senderandrecipientcannot be the zero address.sendermust have a balance of at leastamount.the caller must have allowance for
sender's tokens of at leastamount.
increaseAllowance(address spender, uint256 addedValue) → bool public
Atomically increases the allowance granted to spender by the caller.
This is an alternative to approve that can be used as a mitigation forproblems described in IERC20.approve.
Emits an Approval event indicating the updated allowance.
Requirements:
spendercannot be the zero address.
decreaseAllowance(address spender, uint256 subtractedValue) → bool public
Atomically decreases the allowance granted to spender by the caller.
This is an alternative to approve that can be used as a mitigation forproblems described in IERC20.approve.
Emits an Approval event indicating the updated allowance.
Requirements:
spendercannot be the zero address.spendermust have allowance for the caller of at leastsubtractedValue.
_transfer(address sender, address recipient, uint256 amount) internal
Moves tokens amount from sender to recipient.
This is internal function is equivalent to transfer, and can be used toe.g. implement automatic token fees, slashing mechanisms, etc.
Emits a transfer event.
Requirements:
sendercannot be the zero address.recipientcannot be the zero address.sendermust have a balance of at leastamount.
_mint(address account, uint256 amount) internal
Creates amount tokens and assigns them to account, increasingthe total supply.
Emits a transfer event with from set to the zero address.
Requirements:
tocannot be the zero address.
_burn(address account, uint256 amount) internal
Destroys amount tokens from account, reducing thetotal supply.
Emits a transfer event with to set to the zero address.
Requirements:
accountcannot be the zero address.accountmust have at leastamounttokens.
_approve(address owner, address spender, uint256 amount) internal
Sets amount as the allowance of spender over the owner s tokens.
This internal function is equivalent to approve, and can be used toe.g. set automatic allowances for certain subsystems, etc.
Emits an Approval event.
Requirements:
ownercannot be the zero address.spendercannot be the zero address.
_setupDecimals(uint8 decimals_) internal
Sets decimals to a value other than the default one of 18.
| This function should only be called from the constructor. Mostapplications that interact with token contracts will not expectdecimals to ever change, and may work incorrectly if it does. |
_beforeTokenTransfer(address from, address to, uint256 amount) internal
Hook that is called before any transfer of tokens. This includesminting and burning.
Calling conditions:
when
fromandtoare both non-zero,amountoffrom's tokenswill be to transferred toto.when
fromis zero,amounttokens will be minted forto.when
tois zero,amountoffrom's tokens will be burned.fromandtoare never both zero.
To learn more about hooks, head to Using Hooks.
