Private vs internal cheaper

Question

I know that external is cheaper than public due to how arguments are parsed. Is making a function private or internal cheaper?

Answer 1

I have just checked with a small example in JavaScript VM environment of Remix using the following contract:

contract test {

    function calc(uint256 a, uint256 b) private returns (uint256) {
        return a + b;
    }

    function test(uint256 a, uint256 b) public returns (uint256) {
        return calc(a, b);
    }
}

Changing the visibility of calc from private to internal does not change the cost of gas when calling test.

However, I have done a 2nd test by putting the two version of calc in one contract, i.e. calc1 as private and calc2 as internal.

Then the function defined first in the source code shows a slightly lower gas consumption, however, this is not linked to its visibility. If the first function is private, it's cheaper. And if internal heads the code, it's vice versa.

So I come to the conclusion that gas cost are the same. This would also be in line with my understanding that the distinction between private and internal isn't relevant anymore after the code has been compiled.

Answer 2

https://solidity.readthedocs.io/en/latest/contracts.html?highlight=private

internal: Those functions and state variables can only be accessed internally (i.e. from within the current contract or contracts deriving from it), without using this. private: Private functions and state variables are only visible for the contract they are defined in and not in derived contracts.