How to create a variable in storage via the solidity assembler

Question

Similar to this question How to get access to the storage array through the solidity assembler?

But instead of accessing a storage variable, I want to create a new storage variable via assembly. That means instead of declaring a variable, I use a function to generate the variable.

Instead of:

contract MetaCoin{
 uint A;
}

Do this:

contract MetaCoin{
 function createVariableA(){
  //assembler code here
 }
}

After generating the variable, other functions can somehow use it like a normal declared variable.

Is this possible?

Answer 1

I assume that you need to pass the value of the variable as an attribute of the function:

Remember that sstore saves the variable value in slots. I created two functions to see how it works.

pragma solidity ^0.5.8;

contract MetaCoin {
    function createVariable(uint _x) public  {
        assembly {
            let v := _x
            sstore(0, v)
            let w := add(_x,1)
            sstore(1, w)
        }
    }

    function getVariable() public view returns (uint r, uint s) {
        assembly{
            r := sload(0)
            s := sload(1)
        }
    }

    function addValue(uint _y) public returns (uint t){
        assembly{
            t := add(_y,sload(0))
            sstore(0,t)
        }
    }
}