# Remix Warning: Function state mutability can be restricted to pure

Which is the best, view or pure instead of constant?

``````library SafeMath {
function mul(uint256 a, uint256 b) internal constant returns (uint256) {
uint256 c = a * b;
assert(a == 0 || c / a == b);
return c;
}

function div(uint256 a, uint256 b) internal constant returns (uint256) {
assert(b > 0); // Solidity automatically throws when dividing by 0
uint256 c = a / b;
assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}

function sub(uint256 a, uint256 b) internal constant returns (uint256) {
assert(b <= a);
return a - b;
}

function add(uint256 a, uint256 b) internal constant returns (uint256) {
uint256 c = a + b;
assert(c >= a);
return c;
}
}
``````

thanks

• Question doesn't show research effort. Please make sure you visit the available documentations before putting the question. Nov 22, 2018 at 6:10
• Disagree with the Downvote. This question could also have been a one-liner, and it would still have been of value. It gives an example, which is some effort as such. And the answers show that this one-line question gives many insights. Jan 6 at 19:06

## 3 Answers

View can be used to with a function that does not modify the state but reads state variables.

Pure should be used with functions that neither modify state nor read ( access) state variables. They generally perform operations based on input params.

An example illustrating the same is here:

``````pragma solidity ^0.4.24;

contract ViewVsPure {
uint public age = 18;

function addToAge(uint _no) public view returns (uint){
return age + _no;
}

function add(uint _a, uint _b) public pure returns (uint) {
return _a + _b;
}
}
``````

They're not the same.

`view` functions have read-only access permission on state variables.

`pure` functions do not.

Those functions that you mention can all be declared `pure`.

Side note: this library is provided in OpenZeppelin GitHub as open source, which means that it has been viewed, tested and verified thoroughly. No reason to implement it yourself.

• yes but whats the more secure or convenient Nov 21, 2018 at 8:32
• @upracha: You should choose the most strict option (and the compiler will warn you if you don't anyway). Nov 21, 2018 at 8:33

I think you cant find what you are looking for in the solidity official documentation here: https://solidity.readthedocs.io/en/v0.4.25/contracts.html?highlight=view%20pure#view-functions

Hope it helps