Lesson 3: 03:15:42 confusion with syntax

[3toe]

Lookin for some guidance with about a minute worth of video and a line of the code. In the intial example, when Patrick was saving instances of the simplestorage contract into a variable, he did it like this:

contract StorageFactory{
    SimpleStorage public simpleStorage;

    function createSimpleStorageContract() public {
        simpleStorage = new SimpleStorage();

I get this, putting the contract in a variable. But then to create an array to allow all instances of SimpleStorage.sol to be put into a variable, he uses:

contract StorageFactory{
    SimpleStorage[] public simpleStorageArray;

  function createSimpleStorageContract() public {
        SimpleStorage simpleStorage = new SimpleStorage(); //I don't get this line 
        simpleStorageArray.push(simpleStorage);

I don't get SimpleStorage simpleStorage = new SimpleStorage(); What does that first "SimpleStorage" do?

[RoboCrypter]

@3toe : Let me clear this line and function in easy terms : SimpleStorage simpleStorage = new SimpleStorage();

The public function createSimpleStorageContract does two things: In the first line,

It creates a variable called simpleStorage with the type of SimpleStorage contract.

It does this with the new keyword. When Solidity sees the 'new' keyword here in this context, it says "aha! We're going to deploy a new SimpleStorage contract."

In the second line, it pushes this new contract into the simpleStorageArray array.

[3toe]

Thank you for this breakdown, @abossofmyself ! Very helpful.

So in the first example

    function createSimpleStorageContract() public {
        simpleStorage = new SimpleStorage();

Why didn't he do:

    function createSimpleStorageContract() public {
        SimpleStorage simpleStorage = new SimpleStorage();

?

[othaime-en]

Hey @3toe the line SimpleStorage simpleStorage = new SimpleStorage(); simply does what simpleStorage = new SimpleStorage(); does which creates a new instance of SimpleStorage. The only difference here is that we append the type SimpleStorage. This type is similar to how we write uint256 or int or bool. So answer your question, what SimpleStorage does in that line is specify the type of the contact instance we are creating

[3toe]

@othaime-en Perfect explanation, I got it after you gave the example of uint256, etc..

One follow-up though: So why did we append the type "SimpleStorage" in the second example, but not the first?

[othaime-en]

Hey @3toe in as much as the first example was okay, the most correct way to initialize a variable is by specifying the type. That's why most of the variable declarations you'll see will be like uint256 someVariable. If you continue with the course, you'll see that the we retain the second example not the first. The first was just a simple step towards explaining what was happening.