Mastering Blockchain Programming with Solidity

The _checkOnERC721Received internal function

The _checkOnERC721Received() function is an internal function that is responsible for further calling the onERC721Received() function on an ERC721Receiver contract. Here, the ERC721 contract is behaving like a proxy to the ERC721Receiver contract. If the recipient is not a contract account, the function simply returns true.

The function takes the following arguments:

• from: The address of the current owner of the NFT
• to: The address of the recipient of the NFT
• tokenId: The tokenId of the NFT that is to be transferred

Let's look at the _checkOnERC721Received() function definition:

function _checkOnERC721Received(address from, address to, uint256 tokenId,     bytes memory _data)    internal returns