web3.js Contract returning null instead of an array

Question

Simple contract:

contract ex {
   address[] users;
   function addUser() public {
        users.push(msg.sender);
   }

   function returnUsers() constant returns (address[]) {
       return users;
   }
}

In web3js I have the contract instance exInstance:

var abi = { /* some ABI */ };
var exInstance = web3.eth.contract(abi).at(someaddress);

function getUsers(){
   let users = exInstance.returnUsers.call();
}

And the result is that users is a null. Tried async:

function getUsers(){
   exInstance.returnUsers.call(function(error, users)
      /// some actions
}

But still null.

Am I doing something wrong or I just should iterate it in web3js and in contract just use something like returnUsers(uint i) constant returns (address) { return users[i]; } ?

Answer 1

It is possible to return dynamically sized arrays from external transactions or calls. An external call/transaction is initiated by something outside of the contract code running in the EVM. (Source)

Can you return an array or a string from a solidity function call?

Yes. See array_receiver_and_returner.sol.

What is problematic, though, is returning any variably-sized data (e.g. a variably-sized array like uint[]) from a fuction called from within Solidity. This is a limitation of the EVM and will be solved with the next protocol update.

Returning variably-sized data as part of an external transaction or call is fine.

I'm not sure what is wrong with your code. It works for me in remix.