Mixed visibility (Lesson 9: Hardhat Smart Contract Lottery)

[02b2]

Hi can someone please help me to understand the reason for the mixed visibility on s_players
in the state variable the visibilty for s-players array is private. how ever in the functuion getPlayer, which points to s_players, it is now public, im having trouble understanding why this is.

thanks in advance :) :) :)

(from state variables Raffle.sol line 46)
address payable[] private s_players;

(from function getPlayer Raffle.sol line 190
function getPlayer(uint256 index) public view returns (address) {
return s_players[index];

[javierdash]

Hi! not only that one.
We are making all variables private:

uint private immutable i_entranceFee;
address payable[] private s_players;
VRFCoordinatorV2Interface private immutable i_vrfCoordinator;
bytes32 private immutable i_gasLane;
uint64 private immutable i_subscriptionId;
uint32 private immutable i_callbackGasLimit;
uint16 private constant REQUEST_CONFIRMATIONS = 3;
uint32 private constant NUM_WORDS = 1;

[02b2]

yea your right i only picked one just to make my question short but sweet, but yes this is why i cannot understand why the function is public, yet the state variable is private, is this mixed visibility correct, if so why, or would it in actual fact be considered a bug that could potentially be exploited by someone with good knowledge of the code.

[PatrickAlphaC]

Summary

1. It's useful for devs to know if a function is storage, immutable, or constant for gas purposes.
2. We want a user-friendly function for developers who interact with our application. getPlayer(0) is much nicer than s_players[0].

More information

1. It's useful for devs to know if a function is storage, immutable, or constant for gas purposes.

Giving engineers a visual signal of "oh, this is a storage variable, maybe I shouldn't read and write to it a lot" has proved helpful.

2. We want a user-friendly function for developers who interact with our application. getPlayer(0) is much nicer than s_players[0]

...and it reveals internal implementation details about the contract that a developer shouldn't need to know about. For example, an aggregator would call it s_latestAnswer because it actually stores the value but the proxy would read it from the aggregator so it would just be a method and just call it latestAnswer. To avoid tying our external API to our internal implementation, we just require internal stays internal and you have to always explicitly expose the external API.

This has the added benefit of enforcing that we write natspec docs for all public getters.

[02b2]

thank you so much for the reply and your time Patrick, but what i actually meant was, and maybe its me missnaming it, the private, public, internal, external ....are these called visibilities

im trying to understand why s_players in the state variable is marked as private (address payable[] private s_players;)

yet in the function its marked as public (function getPlayer(uint256 index) public view returns (address) { return s_players[index]; }

as i dont understand why atm, it says to me when i read the code in laymens terms, in the state variable, s_players is private, noone can view it but this contract, then in the function, we contradict ourselves and say actually no!, s_players can now be public, anyone can call it and view it, and why does this not conflict having one be private and one public, should the state variable not be public also

(from state variables Raffle.sol line 46)
address payable[] private s_players;

(from function getPlayer Raffle.sol line 190
function getPlayer(uint256 index) public view returns (address) {
return s_players[index];

[PatrickAlphaC]

Looks like my answer wasn't clear, I was trying to answer that ahah.

So our private s_players array means that no one can call s_players

However, our public getPlayer means that anyone can call getPlayer

If we make a variable private, it just means that only functions in the contract can access that private variable. And then if we choose to make a function in the contract expose that "private" variable... we are free to do so.

Summary

• private means only functions inside the contract can access it.
• But if you wanted to make a function (inside the contract) public... well you can do that.

Does that make sense?

[PatrickAlphaC]

It feels a little silly, but that's why I gave that longer explainer above, to explain why it feels silly, but it's really not.

[02b2]

aha....right ok yes that makes sense ....i feel a bit silly now that i understand it i just had a facepalm moment hahaha

thank you so much for taking that time to explain this its the only thing so far ive not been able to wrap my head around, as it just looked like a confliction to me.

[PatrickAlphaC]

No worries! Facepalms are all part of the learning process ahah.