LP-3722: LRC-721 Burnable Extension

Abstract

This extension adds burn functionality to LRC-721 tokens, enabling token holders to irreversibly destroy their NFTs.

Motivation

Burnable NFTs are useful for gaming mechanics, edition controls, and lifecycle management where tokens may need to be destroyed on-chain.

Specification

interface IERC721Burnable is IERC721 {
    /**
     * @dev Destroys `tokenId` owned by the caller.
     */
    function burn(uint256 tokenId) external;
}

Rationale

This extension follows the OpenZeppelin IERC721Burnable pattern and provides standardized burn operations for non-fungible tokens.

Backwards Compatibility

This is a backwards-compatible extension to the LRC-721 interface. All core NFT functionality remains preserved.

Test Cases

Standard tests should cover:

Burn of owned tokenIds by holder
Prevention of unauthorized burns
Emission of Transfer event to zero address

Reference Implementation

See the IERC721Burnable interface in the standard repository:

/standard/src/interfaces/IERC721Burnable.sol

Implementation

LRC-721 Burnable Token Contracts

Location: ~/work/lux/standard/src/tokens/

Core Contracts:

LRC721.sol - Base NFT implementation
ERC721Burnable.sol - Burn extension
ERC721Enumerable.sol - Enumeration support

Burning Implementation:

// Example from ERC721Burnable.sol
function burn(uint256 tokenId) external {
    require(
        _isApprovedOrOwner(_msgSender(), tokenId),
        "Not authorized to burn"
    );
    _burn(tokenId);
}

function _burn(uint256 tokenId) internal {
    address owner = ownerOf(tokenId);

    // Clear approvals
    _approve(address(0), tokenId);

    // Remove from owner balance
    _balances[owner] -= 1;
    delete _owners[tokenId];

    // Emit transfer to zero address
    emit Transfer(owner, address(0), tokenId);
}

Testing:

cd ~/work/lux/standard
forge test --match-contract ERC721BurnableTest
forge coverage --match-contract ERC721Burnable

Gas Costs

Operation	Gas Cost	Notes
burn (owner)	~45,000	Token removal + event
burn (approved)	~48,000	Approval check + removal

Upgradeable Variants

For proxy-based upgradeable contracts:

Contract	Description
`ERC721BurnableUpgradeable.sol`	Upgradeable burnable

Usage: Initialize in initialize() instead of constructor. See OpenZeppelin Upgrades.

Security Considerations

Ensure only token owner or approved operator can call burn.
Emit Transfer event with zero address to comply with LRC-721 spec.
Clear all approvals before burning to prevent lingering permissions.
Verify token exists before burning (check ownership).

LRC-721 Burnable Extension