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ERC721

Git Source

Inherits: Context, ERC165, IERC721, IERC721Metadata, IERC721Errors

Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including the Metadata extension, but not including the Enumerable extension, which is available separately as {ERC721Enumerable}.

State Variables​

_name​

string private _name;

_symbol​

string private _symbol;

_owners​

mapping(uint256 tokenId => address) internal _owners;

_balances​

mapping(address owner => uint256) private _balances;

_tokenApprovals​

mapping(uint256 tokenId => address) private _tokenApprovals;

_operatorApprovals​

mapping(address owner => mapping(address operator => bool)) private _operatorApprovals;

Functions​

_initialize​

Initializes the contract by setting a name and a symbol to the token collection.

function _initialize(string memory name_, string memory symbol_) internal;

supportsInterface​

See IERC165-supportsInterface.

function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool);

balanceOf​

See IERC721-balanceOf.

function balanceOf(address owner) public view virtual returns (uint256);

ownerOf​

See IERC721-ownerOf.

function ownerOf(uint256 tokenId) public view virtual returns (address);

name​

See IERC721Metadata-name.

function name() public view virtual returns (string memory);

symbol​

See IERC721Metadata-symbol.

function symbol() public view virtual returns (string memory);

tokenURI​

See IERC721Metadata-tokenURI.

function tokenURI(uint256 tokenId) public view virtual returns (string memory);

_baseURI​

Base URI for computing tokenURI. If set, the resulting URI for each token will be the concatenation of the baseURI and the tokenId. Empty by default, can be overridden in child contracts.

function _baseURI() internal view virtual returns (string memory);

approve​

See IERC721-approve.

function approve(address to, uint256 tokenId) public virtual;

getApproved​

See IERC721-getApproved.

function getApproved(uint256 tokenId) public view virtual returns (address);

setApprovalForAll​

See IERC721-setApprovalForAll.

function setApprovalForAll(address operator, bool approved) public virtual;

isApprovedForAll​

See IERC721-isApprovedForAll.

function isApprovedForAll(address owner, address operator) public view virtual returns (bool);

transferFrom​

See IERC721-transferFrom.

function transferFrom(address from, address to, uint256 tokenId) public virtual;

safeTransferFrom​

See IERC721-safeTransferFrom.

function safeTransferFrom(address from, address to, uint256 tokenId) public;

safeTransferFrom​

See IERC721-safeTransferFrom.

function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) public virtual;

_ownerOf​

Returns the owner of the tokenId. Does NOT revert if token doesn't exist IMPORTANT: Any overrides to this function that add ownership of tokens not tracked by the core ERC721 logic MUST be matched with the use of _increaseBalance to keep balances consistent with ownership. The invariant to preserve is that for any address a the value returned by balanceOf(a) must be equal to the number of tokens such that _ownerOf(tokenId) is a.

function _ownerOf(uint256 tokenId) internal view virtual returns (address);

_getApproved​

Returns the approved address for tokenId. Returns 0 if tokenId is not minted.

function _getApproved(uint256 tokenId) internal view virtual returns (address);

_isAuthorized​

Returns whether spender is allowed to manage owner's tokens, or tokenId in particular (ignoring whether it is owned by owner). WARNING: This function assumes that owner is the actual owner of tokenId and does not verify this assumption.

function _isAuthorized(address owner, address spender, uint256 tokenId) internal view virtual returns (bool);

_checkAuthorized​

Checks if spender can operate on tokenId, assuming the provided owner is the actual owner. Reverts if spender does not have approval from the provided owner for the given token or for all its assets the spender for the specific tokenId. WARNING: This function assumes that owner is the actual owner of tokenId and does not verify this assumption.

function _checkAuthorized(address owner, address spender, uint256 tokenId) internal view virtual;

_increaseBalance​

Unsafe write access to the balances, used by extensions that "mint" tokens using an ownerOf override. NOTE: the value is limited to type(uint128).max. This protect against _balance overflow. It is unrealistic that a uint256 would ever overflow from increments when these increments are bounded to uint128 values. WARNING: Increasing an account's balance using this function tends to be paired with an override of the {_ownerOf} function to resolve the ownership of the corresponding tokens so that balances and ownership remain consistent with one another.

function _increaseBalance(address account, uint128 value) internal virtual;

_update​

Transfers tokenId from its current owner to to, or alternatively mints (or burns) if the current owner (or to) is the zero address. Returns the owner of the tokenId before the update. The auth argument is optional. If the value passed is non 0, then this function will check that auth is either the owner of the token, or approved to operate on the token (by the owner). Emits a {Transfer} event. NOTE: If overriding this function in a way that tracks balances, see also {_increaseBalance}.

function _update(address to, uint256 tokenId, address auth) internal virtual returns (address);

_mint​

*Mints tokenId and transfers it to to. WARNING: Usage of this method is discouraged, use _safeMint whenever possible Requirements:

  • tokenId must not exist.
  • to cannot be the zero address. Emits a {Transfer} event.*
function _mint(address to, uint256 tokenId) internal;

_safeMint​

*Mints tokenId, transfers it to to and checks for to acceptance. Requirements:

  • tokenId must not exist.
  • If to refers to a smart contract, it must implement IERC721Receiver-onERC721Received, which is called upon a safe transfer. Emits a {Transfer} event.*
function _safeMint(address to, uint256 tokenId) internal;

_safeMint​

Same as _safeMint, with an additional data parameter which is forwarded in {IERC721Receiver-onERC721Received} to contract recipients.

function _safeMint(address to, uint256 tokenId, bytes memory data) internal virtual;

_burn​

*Destroys tokenId. The approval is cleared when the token is burned. This is an internal function that does not check if the sender is authorized to operate on the token. Requirements:

  • tokenId must exist. Emits a {Transfer} event.*
function _burn(uint256 tokenId) internal;

_transfer​

*Transfers tokenId from from to to. As opposed to transferFrom, this imposes no restrictions on msg.sender. Requirements:

  • to cannot be the zero address.
  • tokenId token must be owned by from. Emits a {Transfer} event.*
function _transfer(address from, address to, uint256 tokenId) internal;

_safeTransfer​

*Safely transfers tokenId token from from to to, checking that contract recipients are aware of the ERC721 standard to prevent tokens from being forever locked. data is additional data, it has no specified format and it is sent in call to to. This internal function is like safeTransferFrom in the sense that it invokes {IERC721Receiver-onERC721Received} on the receiver, and can be used to e.g. implement alternative mechanisms to perform token transfer, such as signature-based. Requirements:

  • tokenId token must exist and be owned by from.
  • to cannot be the zero address.
  • from cannot be the zero address.
  • If to refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer. Emits a {Transfer} event.*
function _safeTransfer(address from, address to, uint256 tokenId) internal;

_safeTransfer​

Same as _safeTransfer, with an additional data parameter which is forwarded in {IERC721Receiver-onERC721Received} to contract recipients.

function _safeTransfer(address from, address to, uint256 tokenId, bytes memory data) internal virtual;

_approve​

Approve to to operate on tokenId The auth argument is optional. If the value passed is non 0, then this function will check that auth is either the owner of the token, or approved to operate on all tokens held by this owner. Emits an {Approval} event. Overrides to this logic should be done to the variant with an additional bool emitEvent argument.

function _approve(address to, uint256 tokenId, address auth) internal;

_approve​

Variant of _approve with an optional flag to enable or disable the {Approval} event. The event is not emitted in the context of transfers.

function _approve(address to, uint256 tokenId, address auth, bool emitEvent) internal virtual;

_setApprovalForAll​

*Approve operator to operate on all of owner tokens Requirements:

  • operator can't be the address zero. Emits an {ApprovalForAll} event.*
function _setApprovalForAll(address owner, address operator, bool approved) internal virtual;

_requireOwned​

Reverts if the tokenId doesn't have a current owner (it hasn't been minted, or it has been burned). Returns the owner. Overrides to ownership logic should be done to _ownerOf.

function _requireOwned(uint256 tokenId) internal view returns (address);

_checkOnERC721Received​

Private function to invoke IERC721Receiver-onERC721Received on a target address. This will revert if the recipient doesn't accept the token transfer. The call is not executed if the target address is not a contract.

function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory data) private;

Parameters

NameTypeDescription
fromaddressaddress representing the previous owner of the given token ID
toaddresstarget address that will receive the tokens
tokenIduint256uint256 ID of the token to be transferred
databytesbytes optional data to send along with the call