ERC20Permit

Git Source

Inherits: ERC20, IERC20Permit, EIP712

Implementation of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].

Adds the permit method, which can be used to change an account's ERC20 allowance (see IERC20.allowance) by presenting a message signed by the account. By not relying on [IERC20.approve](/main/contracts/docs/src/external/OlympusERC20.sol/interface.IERC20#approve), the token holder account doesn't need to send a transaction, and thus is not required to hold Ether at all.

Available since v3.4.

Constants

_PERMIT_TYPEHASH

bytes32 private immutable _PERMIT_TYPEHASH =
        keccak256(
            "Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
        );

State Variables

_nonces

mapping(address => Counters.Counter) private _nonces;

Functions

constructor

Initializes the EIP712 domain separator using the name parameter, and setting version to "1".

It's a good idea to use the same name that is defined as the ERC20 token name.

constructor(string memory name) EIP712(name, "1");

Parameters

Name	Type	Description
name	string

permit

See IERC20Permit.permit.

function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual override;

Parameters

Name	Type	Description
owner	address
spender	address
value	uint256
deadline	uint256
v	uint8
r	bytes32
s	bytes32

nonces

See IERC20Permit.nonces.

function nonces(address owner) public view virtual override returns (uint256);

Parameters

Name	Type	Description
owner	address

Returns

Name	Type	Description
<none>	uint256

DOMAIN_SEPARATOR

See IERC20Permit.DOMAIN_SEPARATOR.

function DOMAIN_SEPARATOR() external view override returns (bytes32);

Returns

Name	Type	Description
<none>	bytes32

_useNonce

"Consume a nonce": return the current value and increment.

Available since v4.1.

function _useNonce(address owner) internal virtual returns (uint256 current);

Parameters

Name	Type	Description
owner	address

Returns

Name	Type	Description
current	uint256