Why people use public function that just calls an internal function?

Question

After user for a long time codes from Open zeppelin I found comething weird. Usually, they use public functions which only use is to call an internal function with the same name but with _ in front.

function transferOwnership(address _newOwner) public onlyOwner {
    _transferOwnership(_newOwner);
}

function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0), "Adress can't be 0x0000...");
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
}

This repeats in a lot of contracts. Why do they do that? Is it a security thing or am I missing something. For me right now, the only thing that this gives me is more gas cost.

Answer 1

Open Zeppelin's contracts are often structured to be editable/extendable, as opposed to what might be considered a "normal coding style".

Perhaps you want to perform some additional checks before transferring ownership (such as before/after a certain date, check that the contract is in a certain state, etc). These checks are specific to your requirement, and have little to do with the actual action of an ownership change. Thus, Open Zeppelin tends to split up the entry and the action in a manner that it's easy to extend functionality in a readable way, without accidentally breaking the actual action being performed.

You will see similar patterns in other base contracts by them, such as the Crowdsale.