This standard is an extension of EIP-1155. It proposes an additional function, ownerOf, which allows EIP-1155 tokens to support Non-Fungibility (unique owners). By implementing this extra function, EIP-1155 tokens can benefit from EIP-721's core functionality without implementing the (less efficient) EIP-721 specification in the same contract.
Currently, EIP-1155 does not allow an external caller to detect whether a token is truly unique (can have only one owner) or fungible. This is because EIP-1155 do not expose a mechanism to detect whether a token will have its supply remain to be "1". Furthermore, it does not let an external caller retrieve the owner directly on-chain.
The EIP-1155 specification does mention the use of split id to represent non-fungible tokens, but this requires a pre-established convention that is not part of the standard, and is not as simple as EIP-721's ownerOf.
The ability to get the owner of a token enables novel use-cases, including the ability for the owner to associate data with it.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
The ownerOf(uint256 tokenId) function MAY be implemented as pure or view.
The supportsInterface method MUST return true when called with 0x6352211e.
ownerOf does not throw when a token does not exist (or does not have an owner). This simplifies the handling of such a case. Since it would be a security risk to assume all EIP-721 implementation would throw, it should not break compatibility with contract handling EIP-721 when dealing with this EIP-1155 extension.
This EIP is fully backward compatible with EIP-1155.
Needs discussion.
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