Sample Account Registry utility

RegisterAccount.sol

pragma solidity ^0.4.24;

contract ERC20_Utility {
  function transfer(address _sender, address _to, uint _amt) external returns (bool);
}

contract RegisterAccount {

  // Maps addresses to registry status
  mapping (address => bool) public registered;

  /**
   * @dev Meta-ERC20-Transfer function. Requires that _to is a registered address
   * @param _token The ERC20_Utility compatible token in which the transfer is being performed
   * @param _to The intended recipient of the token transfer
   * @param _amt The amount of tokens to transfer
   * @return bool Whether the transfer was successful
   */
  function transferERC20(address _token, address _to, uint _amt) external returns (bool) {
    // Ensure the destination is registered
    require(registered[_to], "Destination not registered!");

    // Register the sender, if they are not registered already
    if (!registered[msg.sender]) {
      registered[msg.sender] = true;
    }

    // Perform the transfer, ensure it returns 'true'
    require(ERC20_Utility(_token).transfer(msg.sender, _to, _amt));
    return true;
  }

  /**
   * @dev Allows an account to register themselves
   */
  function registerAccount() external {
    require(!registered[msg.sender]);
    registered[msg.sender] = true;
  }
}