Error in external function parameter defination for an interface

Question

Dear community members,

I have come across an error while defining an interface (just using the standard one interface ERC721TokenReceiver)

this interface is mentioned in this link https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md

I was receving below error (Please find the screenshot) Data location must be "calldata" for parameter in external function, but none was given.

the strange part was when I have changed bytes to bytes32 then error had gone. But I m in doubt

1) What was the reason for error

2) should i deviate from std guideline for defining the interface

Br Dev

Answer 1

bytes is an array of byte (like byte[], only easier on the eyes), so the second explicitness requirement listed here applies: https://solidity.readthedocs.io/en/v0.5.0/050-breaking-changes.html#explicitness-requirements

You can compile it, as is, with an earlier Solidity version. I found no issue with 0.4.20 and 0.4.25.

Alternatively, you can refactor the code slightly.

Change the first line to pragma solidity 0.5.2;, and at line 15, ... bytes calldata _data, .... That will work with a 0.5.2 compiler.

Hope it helps.