How to unpack Tuple to Struct in Solidity?

Question

I saw a similar question here which I tried to use in my example but I still get confused from the code. Can you tell me what is the difference between those two examples?

contract First {

struct Emission {
    string accountIdHash;
    string orderIdHash;
}

function getData(string memory _orderIdHash) public view returns (string memory,string memory)
{
    return (
        "Account1",
        "Order1"
    );
  }
}

interface IFirst {
   function getData(string memory) external view returns (
        string memory,
        string memory
    );
 }

contract Second {

address contractFirst;

struct Emission {
    string accountId;
    string orderId;
}

Emission emission;

constructor(address _addressContractFirst)
{
    contractFirst = _addressContractFirst;
}

function mint(string memory _orderIdHash) public {

 
  (string memory accountIdHash, string memory orderIdHash) = IFirst(contractFirst).getData(_orderIdHash);

   emission = Emission(accountIdHash, orderIdHash);
}
}

And this example:

 function mint(string memory _orderIdHash) public {

 Emission memory emission = Emission(IFirst(contractFirst).getData(_orderIdHash));

 }

For me they are absolutely the same but in the second example Solidity throws an error saying that:
Wrong argument count for struct constructor: 1 arguments given but expected 2.

Answer 1

As the error says, you're passing only one argument (a tuple of 2 elements) to the getData function, while it needs 2 arguments.

And it seems solidity to not expand tuple to arguments.

That's why the first mint function works : first the tuple is broken down into 2 distinct elements accountIdHash and orderIdHash, and then passed as 2 separated arguments.

I found the exact same thing you are trying to do in an issue/feature request on the Solidity Repository : https://github.com/ethereum/solidity/issues/9600

It seems this has been requested, seen by the Solidity team (cameel) but not implemented.