Return null instead of contract

Question

I hava a function in a contract:

  function getLastBidding() public view returns (Bidding) {
    return biddings[biddings.length-1];
  }

The problem is when the biddings array is empty, it doesn't work, because I can't access index -1. So, I would like to return some sort of null when the array is empty. What can I return instead?

Answer 1

Your best bet is to probably require(bidding.length > 0); before returning.

It will revert the request...but that's kind of the point.

Answer 2

Along the lines of @ReyHaynes's suggestion, you can put almost anything into a dynamic array, but you'll get an error if you try to recall row 0 from a list with less than 1 row.

Consider separating concerns by returning the length of the list by itself. That way, if a client requests the first row before it exists, error is the appropriate response. With a public array, the clients can inspect by row number, starting at row 0 (if it exists).

BiddingStructs[] public biddingStructs;

function getBiddingCount() public view returns(uint count) {
    return biddingStructs.length;
}

Hope it helps.