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Summary

ERC-4610 is an extension of ERC-721 and it aims to provide standardized token rental and loanable protocol for ecological applications such as blockchain games. <br/>

Specification

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delegatorOf

Returns the delegator of ERC721.

Delegator is only an attribute of ERC721 for identification, and does not have any direct permissions like {approve} {setApprovalForAll} {transferFrom} {safeTransferFrom}.

function delegatorOf(uint256 tokenId) external view returns (address);

setDelegator

Set _delegator as the delegator of the ERC721 with tokenId as _tokenId.

Emits an {SetDelegator} event.

The delegator attribute can be set to address(0), which means the ERC721 has no delegator.

function setDelegator(address _delegator, uint256 _tokenId) external returns (bool);

safeTransferFrom

Safely transfers tokenId token from from to to and delegator won't be cleared if reserved is true.

function safeTransferFrom(address from, address to, uint256 tokenId, bool reserved) external;
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Implementation

see contracts/ERC4610.sol

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How it works

Application running on the blockchain, such as blockchain game, can be defined as a state machine. Most blockchain games are based on ERC-721, that is, only the owner has the permission to send a valid transaction that can cause state transition, and it's inconvenience in scenarios such as lending.

state

ERC-4610 aims to provide standardized token rental and loanable protocol for ecological applications such as blockchain games. ERC-4610 is an extension of ERC-721. In ERC-721, we use owner to determine who has the unique ownership of NFTs. And in ERC-4610, we added a role called delegator.

delegator has no permission to transefer or approve the token, it's a tag of ERC-721. What the delegaotr can do depends on the design and development of the application or game. In general, without affecting the security of assets, the delegator should have the same permissions as the owner. In this way, the delegator can also send a valid transaction and change the state machine.

Note that delegator is only an operator of owner , therefore, the transaction sent by delegator should eventually change the state of owner, not delegator. When it comes to the transfer of assets, the sender should be the owner (not delegator) or other (depending on your app logic), and when the assets are to be transferred out, the recipient should be the owner or other.

how_it_works

The figure above shows how game or applications that are based on ERC-4610 will achieve the goal of NFTs lending and borrowing in a decentralized way.

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Example

In the contracts/showcase, you will see an example of how to develop your application or game based on ERC-4610.

In the example, gold is the revenue token, and Digimon is the NFT token. There are a total of five methods involing asset flow, and these five methods will be called by the delegator.

1. claim

User can claim gold rewards from the Game.

claim

2. Levelup

User can levelup his NFT level, and it will consume some gold tokens.

levelup

3. breed

User breeds a Digimon, and will get a new Digimon NFT

breed

4. adventure

User's Digimon goes on an adventure, the NFT will transfer to game contract from owner.

adventure

5. home

User withdraws his or her Digimon NFT.

home

Cautions

  1. The developers of ERC-4610 should strictly distinguish between owner and delegator from msg.sender. require(_onlyOwnerOrDelegator(tokenId)) can be used instead of require(_onlyOwner(tokenId)) for identity verification of msg.sender .
  2. The delegator has the permission to send a valid transaction, but does not hold or handle any related assets. When it comes to the transfer of assets, the sender should be the owner (not delegator) or other (depending on your app logic), and when the assets are to be transferred out, the recipient should be the owner or other.
  3. delegator should generally have no permission for functions that may cause the loss of owner assets, such as burning NFTs.
  4. In some cases, the loan contract may not support the transfer of NFTs to the game contract or application contract. Please pay attention to this.
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