USDC v2: Upgrading a $1.4B Token - sload/sstore example

sload-sstore-example.sol

contract Foo {
    bytes32 private constant NUM_SLOT = keccak256("Foo.num");
    
    function num() public view returns (uint256 val) {
        bytes32 slot = NUM_SLOT;
        assembly {
            val := sload(slot)
        }
    }
    
    function setNum(uint256 val) public {
        bytes32 slot = NUM_SLOT;
        assembly {
            sstore(slot, val)
        }
    }
}