Smart Contracts Programming Tutorials, Guides & Best Practices

interface MyInterface {
    function setData(uint _data) external;
    function getData() external view returns (uint);
}

contract MyContract is MyInterface {
    uint private data;

    function setData(uint _data) external override {
        data = _data;
    }

    function getData() external view override returns (uint) {
        return data;
    }
}

Libraries are similar to contracts but are meant to hold reusable code. They cannot hold state.