Some sample code for better understanding the implications of the storage/memory keywords when used in function arg

mem_vs_stor_arguments.sol

pragma solidity ^0.4.18;


// Some sample code for better understanding the implications of the storage/memory keywords 
// when used in function args

library Libby {
    struct Nums {
        uint8 num;
        uint8 num2;
    }
    
    
    function setStorageNums(Nums storage self, uint8 _num, uint8 _num2) internal {
        self.num = _num;
        self.num2 = _num2;
    }
    
    function setMemoryNums(Nums memory self, uint8 _num, uint8 _num2) internal {
        self.num = _num;
        self.num2 = _num2;
    }
}

contract Fun {
    using Libby for Libby.Nums;
    
    Libby.Nums internal storageNums;
    
    function foo() public {
        Libby.Nums memory memoryNums;
        storageNums.setStorageNums(1,2); 
        memoryNums.setStorageNums(1,2); //  TypeError: Member "setStorageNums" is not available in struct Libby.Nums memory outside of storage.
    }
    
    function bar() public {
        Libby.Nums memory memoryNums;
        storageNums.setMemoryNums(1,2);
        memoryNums.setMemoryNums(1,2);
        
    }
}