A Small Doubt from chapter 3 of the tutorial

[ArkX69]

code: SimpleStorage simpleStorage = new SimpleStorage();
can someone pls explain why do we need to put a bracket here with the SimpleStorage?
and why are we declaring the Type 'SimpleStorage' with a new and a bracket?

[krakxn]

Explanation:

First we initialize simpleStorage, a variable (of type SimpleStorage)
then, in our declaration, we instantiate it as a SimpleStorage object with the help of the new keyword
and the brackets are necessary because whenever we instantiate an object, it first calls the constructor of that object
so, empty parameters here means that we are calling the default constructor of SimpleStorage, as our object is of that type
and in the future, you will also see parameterized constructors which are essentially the same but with arguments - and then, in that case, you will see parameters being implemented in the declaration

Hope this helped! Good luck with the course

EDIT: BTW, I would recommend going through basic OOP principles as this is a fundamental concept in Computer Science

[shoaibshebi]

Simply, It's the behavior of OOP.

Contracts ~= Classes

So whenever you inherit Contract, you create their instance same as classes in OOP.

Please go through this link: inheretence in solidity

[ArkX69]

Thanks for the explaination @krakxn , can you help me out with some other doubts as well

from the same chapter this code line is there "
function sfStore(uint256 _simpleStorageIndex, uint256 _simpleStorageNumber) public {
SimpleStorage simpleStorage = simpleStorageArray[_simpleStorageIndex];
simpleStorage.store(_simpleStorageNumber);
}

i cannot under stand why is there .store being used because .store as in the SimpleStorage contract was have a favourite number param so why are we using this and how come this is working

[krakxn]

Next time - please format (you can edit it) your query properly by using three backticks before and after the code, makes reading code much easier!

.store() is used to set favouriteNumber the value of the argument passed to .store() (in this case,) in the main contract. So, if you log out the favouriteNumber before and after you will see that the function has worked correctly in this way:

Example: (not technical/precise to the code - more like English for comprehension)

fav. number is 3
we log out fav. number, we will get 3
we do store(7)
fav. number is now 7
if we log out fav. number now, we will get 7

[ArkX69]

Thanks for the explaination man, got it crystal clear

U and me now best friends :)

[krakxn]

You're welcome! And haha, for sure :)

[Mark-Four]

Exactly what @krakxn said. I'd like to elucidate a bit using another example of inheritance (from https://www.geeksforgeeks.org/solidity-constructors/?ref=lbp)

pragma solidity ^0.5.0;

contract Base {
    uint data;
    constructor(uint _data) public {
      data = _data;  
   }
 }
 
contract Derived is Base(2) {             
     function getData( ) external returns(uint) {
       uint result = data ** 2;
       return result;
   }
}

Notice how when the Derived contract is inheriting the Base Contract, the number '2' is being passed as a constructor argument. This is the argument that the Base contract expects in its constructor, which is a uint. Even though the data variable wasn't initialized or assigned a value in the Base contract, it is automatically recognized to be 2, since it was passed as a constructor argument when the contract was being created.

The point being, that when you say SimpleStorage simpleStorage = new SimpleStorage();

The last parentheses indicate that NO arguments are being passed to the contract constructor when a new SimpleStorage is created.

Hope that helps answer your question. I'm also new but I read this in some really helpful documentation on https://www.geeksforgeeks.org/solidity-constructors/?ref=lbp