Change State Variable Content in Contract A from Contract B

Question

If I have two contracts, contract A and contract B. How can I change the content of a publicly declared state variables in Contract A from Contract B?

Answer 1

It's not important that the variable is public. It implies many things but it doesn't imply that anyone or any contract can come along and overwrite it.

contract A will have to explose a function. contract B will need knowledge of this function as well as knowledge of contract A's address. This is more than one way to address each of those concerns. As a starting point, consider.

In contract A, create a function that actually writes to the state variable.

function setValue(uint newValue) public returns(bool success) {
  someValue = newValue;
  return true;
}

in contract B.sol, inform B about the interface and location of A and instantiate an instance.

contract AInterface {
  function setValue(uint newValue) public returns(bool success);
}

contract B {

  AInterface a;

  function B(address addressContractA) public {
    a = AInterface(addressContractA);
  }

  function setThatThing(uint newNumber) public returns(bool success) {
    return a.setValue(newNumber);
  }
}

Hope it helps.