Hello, World! Pt.2 - Contract constraints

In the Hello, World tutorial, we built a CorDapp allowing us to model IOUs on ledger. Our CorDapp was made up of two elements:

  • An IOUState, representing IOUs on the blockchain
  • An IOUFlow and IOUFlowResponder flow pair, orchestrating the process of agreeing the creation of an IOU on-ledger

However, our CorDapp did not impose any constraints on the evolution of IOUs on the blockchain over time. Anyone was free to create IOUs of any value, between any party.

In this tutorial, we’ll write a contract to imposes rules on how an IOUState can change over time. In turn, this will require some small changes to the flow we defined in the previous tutorial.

We’ll start by writing the contract.