First Smart Contract Example with comments

example-contract.solidity

pragma solidity ^0.4.17;
// specify the version of Solidity that our code is written with

contract Inbox {
    // define a new contract (almost identical to a class) that will
    // have some number of methods and variables

    string public message;
    // - storage variables:
    // declares all of the instance variables (and their types)
    // that will exist in this contract
    // - public defines who have access to that variable
    // - message is the name of the variable --> the value of the variable will be
    // stored in the ethereum blockchain for ethernity
    // IN CONTRAST WITH STORAGE VARIABLES WE HAVE LOCAL VARIABLES WHICH ARE NEVER STORED IN THE BLOCKCHAIN


    function Inbox(string initialMessage) public {
        // this function is called constructor function since it has the same
        // name as the contract.
        // A constructor function is automatically called one time when the
        // contract is created. Invoked automatically when the contract is deployed
        message = initialMessage;

    }

    function setMessage(string newMessage) public {
        // this functions with a different name from the contract's one can be called
        // once the contract has been deployed on the blockchain
        message = newMessage;
        // we are modifying the message variable here so we can't use either constant and view in the function type
    }

    // this function is unuseful since the message variable is public so solidity will
    // create a function for use to return the message variable's value
    function getMessage() public view returns (string) {
        // public and view are the function type declaration
        // most common function types --> [public, private, view, constant, pure, payable]
        return message;
        // we are just accessing data not modifying. This is why we use the view function type
        // so the compiler knows we only access data.
        // - returns (with return's type) can only be specified with functions that have
        // view and constant aas function type.
    }
}