Remix Warning: Function state mutability can be restricted to pure

Question

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

Answer 1

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;
  }
}

Answer 2

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.

Answer 3

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