The proposed standard defines a lightweight interface to expose functional ownership and balances of held tokens. A held token is a token owned by a contract. This standard may be implemented by smart contracts which hold EIP-20, EIP-721, or EIP-1155 tokens and is intended to be consumed by both on-chain and off-chain systems that rely on ownership and balance verification.
As different areas of crypto (DeFi, NFTs, etc.) converge and composability improves, there will more commonly be a distinction between the actual owner (likely a contract) and the functional owner (likely a user) of a token. Currently, this results in a conflict between mechanisms that require token deposits and systems that rely on those tokens for ownership or balance verification.
This proposal aims to address that conflict by providing a standard interface for token holders to expose ownership and balance information. This will allow users to participate in these DeFi mechanisms without giving up existing token utility. Overall, this would greatly increase interoperability across systems, benefiting both users and protocol developers.
Example implementers of this ERC standard include
Example consumers of this ERC standard include
Smart contracts implementing the ERC20 held token standard MUST implement all of the functions in the IERC20Holder interface.
Smart contracts implementing the ERC20 held token standard MUST also implement ERC165 and return true when the interface ID 0x74c89d54 is passed.
Smart contracts implementing the ERC721 held token standard MUST implement all of the functions in the IERC721Holder interface.
Smart contracts implementing the ERC721 held token standard MUST also implement ERC165 and return true when the interface ID 0x16b900ff is passed.
Smart contracts implementing the ERC1155 held token standard MUST implement all of the functions in the IERC1155Holder interface.
Smart contracts implementing the ERC1155 held token standard MUST also implement ERC165 and return true when the interface ID 0xced24c37 is passed.
This interface is designed to be extremely lightweight and compatible with any existing token contract. Any token holder contract likely already stores all relevant information, so this standard is purely adding a common interface to expose that data.
The token address parameter is included to support contracts that can hold multiple token contracts simultaneously. While some contracts may only hold a single token address, this is more general to either scenario.
Separate interfaces are proposed for each token type (EIP-20, EIP-721, EIP-1155) because any contract logic to support holding these different tokens is likely independent. In the scenario where a single contract does hold multiple token types, it can simply implement each appropriate held token interface.
Importantly, the proposed specification is fully compatible with all existing EIP-20, EIP-721, and EIP-1155 token contracts.
Token holder contracts will need to be updated to implement this lightweight interface.
Consumer of this standard will need to be updated to respect this interface in any relevant ownership logic.
A full example implementation including interfaces, a vault token holder, and a consumer, can be found at assets/eip-4987/.
Notably, consumers of the IERC721Holder interface can do a chained lookup for the owner of any specific token ID using the following logic.
Consumers of this standard should be cautious when using ownership information from unknown contracts. A bad actor could implement the interface, but report invalid or malicious information with the goal of manipulating a governance system, game, membership program, etc.
Consumers should also verify the overall token balance and ownership of the holder contract as a sanity check.
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