UsingInterface.sol

💻 The code corresponding to this page can be found on Github at UsingInterface.sol

Let us write the UsingInterface.sol, that will use the Interface_SimpleAddition to call functions on the SimpleAddition contract.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

/* Note that we only import the interface, not the actual contract
   we will be calling.
*/
import {Interface_SimpleAddition} from "./Interface_SimpleAddition.sol";

contract UsingInterface {

    Interface_SimpleAddition public IsimpleAddition;

    constructor(address _simpleAdditionAddress) {
        IsimpleAddition = Interface_SimpleAddition(_simpleAdditionAddress);
    }

    function setA(uint256 _a) public {
        IsimpleAddition.setA(_a);
    }

    function setB(uint256 _b) public {
        IsimpleAddition.setB(_b);
    }

    function returnSumOfStateVariables() public view returns (uint256) {
        return IsimpleAddition.returnSumOfStateVariables();
    }

    function returnSumOfLocalVariables(uint256 _a, uint256 _b) public view returns (uint256) {
        return IsimpleAddition.returnSumOfLocalVariables(_a, _b);
    }

}

A few notes:

1. The UsingInterface contract takes the address of the SimpleAddition contract as a constructor param. This is needed because the actual functions will be called on an already deployed contract.
2. An instance of the Interface_SimpleAddition interface can then be used to call functions on the SimpleAddition contract.
3. If the function declarations in the interface are incorrect, the calls to the underlying contract will fail.

In the final section, we will write a few Foundry tests to check if UsingInterface can call functions on SimpleAddition.