According to ERC-721 interface the function safeTransferFrom seems to be overloaded:

function safeTransferFrom(address _from, address _to, uint256 _tokenId) public;
function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes _data) public;

Why so? Any ideas? Thx!


The one without _data doesn't send any data when it calls the other contract. (It sends a zero-length byte sequence.)

The one with _data does.

  • This is incorrect, the other contract must implement the wallet interface, which has the 3-parameter function onERC721Received(address _from, uint256 _tokenId, bytes data). If you only pass two, the transaction will fail. – AnAllergyToAnalogy Apr 17 '18 at 2:39
  • I'm not sure what part of my answer you think is "incorrect." Could you explain further? Perhaps there's something that could be clarified. (To be clear, I agree with the rest of your comment.) – smarx Apr 17 '18 at 3:05
  • "The one without _data doesn't send any data when it calls the other contract." - technically it should still pass data when it calls the other function, the data is just an empty string (see my answer below). – AnAllergyToAnalogy Apr 17 '18 at 3:08
  • Ah, I'll clarify. – smarx Apr 17 '18 at 3:11

From the ERC-721 draft standard, take note of the code comments in the interface provided.

Specifically, for the safeTransferFrom function without the 4th parameter:

/// @dev This works identically to the other function with an extra data parameter,
///  except this function just sets data to ""

So your three-parameter function should do exactly the same as the four-parameter function, but pass "" as the data.

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