onERC721Recieved implementation

Question

As per the ERC721 requirements, I have to implement onERC721Recieved. This is how I did it:

function onERC721Received(
    address _operator, 
    address _from, 
    uint256 _tokenId, 
    bytes calldata _data
)external returns(bytes4) {
    return bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"));
} 

This seems to be in line with what is required of the function. However, this raises two questions:

1. If this does not actually use any of the parameters, why pass the parameters to the function at all? It is now throwing errors every time I test the contract.
2. What is the reason behind this function?

Answer 1

You can remove the errors with this implementation:

function onERC721Received(
    address, 
    address, 
    uint256, 
    bytes calldata
)external returns(bytes4) {
    return bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"));
} 

The parameters are there for implementations that want to use them. Perhaps for doing an accounting of incoming assets. Or perhaps for denying receipt of certain assets.