Let's assume the following:

  • There is a master contract A, an interface contract IB, and a slave contract B
  • A implements IB to allow upgrading B without redeploying A


Does IB need to have all functions of B, or only the ones used by A?

  • Interfaces don't implement contracts: contracts implement interfaces. What is the inheritance chain here? A->IB->B ? Seems odd and IB doesn't have to implement anything. Or is it an interface I with contracts A and B implementing I? What goes in I would be what you require both A and B to implement: A and B can each have extra functions.
    – eth
    Commented Feb 10, 2017 at 6:15

1 Answer 1


According to my experience in the following code


it is enough implementing those ones you are using. In the example:

/// ---- dataStorage interface
contract dataStorage {
    function getBalanceOf(address _account) constant returns (uint256 balance);
    function setBalanceOf(address _account, uint256 _value);

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