Libraries

In web3 ecosystem in general, libraries take form of the special types of smart-contracts in solidity.

• SafeMath

SafeMath library declaration example ​

library SafeMath {
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }

    // ...sub, mul, div funcions
}

We create a library with library keyword.

Libraries allow us to use the using keyword, which automatically tacks on all of the library's methods to another data type:

using SafeMath for uint;

// now we can use these methods on any uint
uint test = 2;
test = test.mul(3); // test now equals 6
test = test.add(5); // test now equals 11

When we declare using SafeMath for uint, the uint we call the function on (test) is automatically passed in as the first argument.

Basically add just adds 2 uints like +, but it also contains an assert to make sure the sum is greater than a. This protects us from overflows.