👻 SBT

Introduction

The SBT token is an elegantly crafted implementation of a Soul Bound Token, designed for optimal efficiency and minimal resource usage.

Implementation

Given that the token owner is unable to transfer the token to others, certain functionalities, such as approve and transfer, have been excluded intentionally to streamline bytecode. While this departure means that the token does not strictly adhere to the ERC721 standard, the implementation maintains seamless integration with the MetaMask and OpenSea platforms.

Example

To create own Soul Bound Token, start by inheriting from the SBT contract. You can optionally create external functions, such as mint and burn, remembering to apply the onlyOwner modifier.

import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";

import "@solarity/solidity-lib/tokens/ASBT.sol";

contract MySBT is ASBT, OwnableUpgradeable {
    function __MySBT_init(
        string memory name_, 
        string memory symbol_
    ) external initializer {
        __Ownable_init(msg.sender);
        __ASBT_init(name_, symbol_);
    }

    function mint(address to_, uint256 tokenId_) external onlyOwner {
        _mint(to_, tokenId_);
    }

    function burn(uint256 tokenId_) external onlyOwner {
        _burn(tokenId_);
    }
}

After creating and initializing token, it can be used in different contexts.

MySBT public sbt = new MySBT();
sbt.__MySBT_init("MySBT", "MSBT");

sbt.mint(address(1), 0); // address(1) has tokens: [0]
sbt.mint(address(1), 1); // address(1) has tokens: [0, 1]

sbt.burn(0); // address(1) has tokens: [1]

sbt.ownerOf(0); // address(0)
sbt.ownerOf(1); // address(1)

sbt.tokenURI(1); // ""

sbt.setBaseURI("base/");
sbt.tokenURI(1); // "base/1"

sbt.setTokenURI(1, "token1");
sbt.tokenURI(1); // "token1"

To customize the logic of the token, we can use a hook _beforeTokenAction that is called before the mint and burn actions. For instance, the next hook prohibits tokens from being mined to address(this).

contract MySBT is /* ... */ {
    // ...
 
    function _beforeTokenAction(address to_, uint256 tokenId_) internal override {
        require(to_ != address(this), "SBT: can't transfer to the contract itself");
    }
}