Token Swap (swap tokens 1:1 from `old_token_contract` to `new_token_contract`)

TokenSwap.md

Workflow

old_token_contract is ERC20 compliant. new_token_contract is TokenSwap

Token swap contract

import "zeppelin-solidity/contracts/token/ERC20/StandardToken.sol";

contract TokenSwap is StandardToken {
  event Swap(address indexed to, uint256 amount);

  address public old_token_contract;
  
  function TokenSwap(address _old) public {
    old_token_contract = _old;
  }
  
  function swapTokens(uint256 amount) public {
    // require: balanceOf msg.sender in old_token_contract is at least "amount"
    // require: allowance of new_token_contract to spend "amount" tokens of msg.sender
    // require: burn old tokens (transferFrom new_token_contract to 0x0)
    // mint new_token_contract "amount" tokens to msg.sender
  }
  
  function mintTokens(address _to, uint256 _amount) internal {
    // add "amount" to totalSupply_ of this token
    // add "amount" to balances[_to]
  }
}

1. new_token_contract inherits TokenSwap contract

2. Users approve the new_token_contract to spend their old_token_contract tokens

   approve(new_token_contract_address, amount)

3. Users call swapTokens in the TokenSwap.sol contract, with the amount they want to swap

   TokenSwap.swapTokens(amount)