Supported ERC Token Standards

Interact with Hedera Token Service fungible and non-fungible tokens in your Solidity contract using ERC-20 and ERC-721 standards.

ERC-20 (Fungible)

Supported

name

function name() public view returns (string)

Returns the name of the token.

symbol

function symbol() public view returns (string)

Returns the symbol of the token.

decimals

function decimals() public view returns (uint8)

Returns the number of decimals the token uses.

totalSupply

function totalSupply() external view returns (uint256)

Returns the total supply of the token.

balanceOf

function balanceOf(address account) external view returns (uint256)

Returns of the balance of the token in the specified account. The account is the Hedera account ID 0.0.x in Solidity address format or the evm address of a contract that has been created via the CREATE2 operation.

transfer

function transfer(address recipient, uint256 amount) external returns (bool)

Transfer tokens from your account to a recipient account. The recipient is the Hedera account ID 0.0.x in Solidity format or the evm address of a contract that has been created via CREATE2 operation.

allowance

function allowance(address owner, address spender) external view returns (uint256)

Returns the remaining number of tokens that spender will be allowed to spend on behalf of owner through transferFrom. This is zero by default. This value changes when approve or transferFrom are called. This works by loading the owner FUNGIBLE_TOKEN_ALLOWANCES from the accounts ledger and returning the allowance approved for spender The owner and spender address are the account IDs (0.0.num) in solidity format.

approve

function approve(address spender, uint256 amount) external returns (bool)

Sets amount as the allowance of spender over the caller's tokens.

This works by creating a synthetic CryptoApproveAllowanceTransaction with payer - the account that called the precompile (the message sender property of the message frame in the EVM).

Fires an approval event with the following signature when executed: event Approval(address indexed owner, address indexed spender, uint256 value);

transferFrom

function transferFrom(address sender, address recipient, uint256 amount) external returns (bool)

Moves amount tokens from from to to using the allowance mechanism. amount is then deducted from the caller's allowance.

This works by creating a synthetic CryptoTransferTransaction with fungible token transfers with the is_approval property set to true.

ERC-721 (Non-Fungible)

Supported

The following ERC-721 operations will be supported. Standard ERC-721 Events will be emitted as appropriate.

From interface ERC721

balanceOf

function balanceOf(address _owner) external view returns (uint256)

Returns balance of the HTS non fungible token from the account owner. The _owner is the Hedera account ID 0.0.x in Solidity format or the evm address of a contract that has been created via the CREATE2 operation.

ownerOf

function ownerOf(uint256 _tokenId) external view returns (address)

Returns the account ID of the specified HTS token owner. The _tokenId is the Hedera serial number of the NFT.

approve

function approve(address _approved, uint256 _tokenId) external payable

Gives the spender permission to transfer a token (_tokenId) to another account from the owner. The approval is cleared when the token is transferred. The _tokenId is the Hedera serial number of the NFT.

This works by creating a synthetic CryptoApproveAllowanceTransaction with payer - the account that called the precompile (the message sender property of the message frame in the EVM).

If the spender address is 0, this creates a CryptoDeleteAllowanceTransaction instead and removes any allowances previously approved on the token.

Fires an approval event with the following signature when executed:

event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

setApprovalForAll

function setApprovalForAll(address _operator, bool _approved) external

Approve or remove an operator as an operator for the caller. Operators can call transferFrom for any token owned by the caller.

This works by creating a synthetic CryptoApproveAllowanceTransaction with payer - the account that called the precompile (the message sender property of the message frame in the EVM).

getApproved

function getApproved(uint256 _tokenId) external view returns (address)

Returns the account approved for the specified _tokenId. The _tokenId is the Hedera serial number of the NFT.

This works by loading the SPENDER property of the token from the NFTs ledger.

isApprovedForAll

function isApprovedForAll(address _owner, address _operator) external view returns (bool)

Returns if the operator is allowed to manage all of the assets of owner.

This works by loading the APPROVE_FOR_ALL_NFTS_ALLOWANCES property of the owner account and verifying if the list of approved for all accounts contains the account id of the operator.

transferFrom

function transferFrom(address _from, address _to, uint256 _tokenId) external payable

Transfers a token (_tokenId) from a Hedera account (from) to another Hedera account (to) in Solidity format. The _tokenId is the Hedera serial number of the NFT.

This works by creating a synthetic CryptoTransferTransaction with nft token transfers with the is_approval property set to true.

From interface ERC721Metadata

name

function name() external view returns (string _name)

Returns the name of the HTS non fungible token.

symbol

function symbol() external view returns (string _symbol)

Returns the symbol of the HTS non fungible token.

tokenURI

function tokenURI(uint256 _tokenId) external view returns (string)

Returns the token metadata of the HTS non fungible token. This corresponds to the NFT meta data field when minting an NFT using HTS. The _tokenId is the Hedera serial number of the NFT.

From interface ERC721Enumerable

totalSupply

function totalSupply() external view returns (uint256)

Returns the total supply of the HTS non-fungible token.

Not Supported

The following ERC-721 operations are currently not supported.

From interface ERC721

  • safeTransferFrom

All semantics of interface ERC721TokenReceiver.

  • Existing Hedera token association rules will take the place of such checks.

From interface ERC721Enumerable

  • tokenByIndex

  • tokenOfOwnerByIndex

Examples

References

PreviousSolidity Variables and OpcodesNextHedera Services Integration with Smart Contracts

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