Solidity 101: Interfaces, Error Handling, and Libraries

Solidity 101: Interfaces, Error Handling, and Libraries

Delving Further into Solidity

Jun 4, 2023·

3 min read

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In the previous posts, we've introduced Solidity and explored some fundamental and advanced concepts related to Ethereum's smart contract language.

Now, let's go further and dig into more complex topics: interfaces, error handling, and using libraries.


Interfaces in Solidity define a contract's external functions and can be used to interact with other contracts. They provide a way to abstract contract functionalities and allow contracts to work together in a type-safe manner.

Here's a simple interface and its implementation:

pragma solidity >=0.7.0 <0.9.0;

interface Greeter {
    function greet() external pure returns (string memory);

contract HelloGreeter is Greeter {
    function greet() external pure override returns (string memory) {
        return "Hello, World!";

The Greeter interface defines a greet function, and HelloGreeter contract implements this function. Interfaces can be particularly useful when interacting with external contracts that adhere to standard patterns, like ERC20 or ERC721 in Ethereum.

Error Handling

Solidity uses state-reverting exceptions to handle errors. The require, assert, and revert functions are used to throw exceptions:

  • require: Checks for valid conditions and throws an exception if the condition is not met. Typically used for checking inputs of a function.

  • assert: Used for internal error checking. A failed assertion likely signifies a bug in your contract.

  • revert: Similar to require, but also allows you to provide a custom error message.

pragma solidity >=0.7.0 <0.9.0;

contract SafeDivision {
    function divide(uint256 a, uint256 b) public pure returns (uint256) {
        require(b > 0, "Divider cannot be zero");
        uint256 result = a / b;
        assert(result * b == a);
        return result;

In the SafeDivision contract above, require is used to prevent division by zero, and assert is used to verify that the division operation was correct.


Solidity libraries are similar to contracts, but they can't have state variables or receive Ether.

Libraries are typically used to move complex operations or reusable functions out of your contracts. Here's an example of a library and a contract that uses it:

pragma solidity >=0.7.0 <0.9.0;

library SafeMath {
    function add(uint a, uint b) internal pure returns (uint) {
        uint c = a + b;
        require(c >= a, "Addition overflow");

        return c;

contract MyContract {
    using SafeMath for uint;

    uint public value;

    function increment(uint _value) public {
        value = value.add(_value);

In this example, SafeMath is a library that provides a safe add function that prevents integer overflow.

MyContract then uses this function to safely increment its value state variable.


Mastering Solidity is a journey, and it's vital to understand the language's more complex aspects as you develop more sophisticated smart contracts.

Always remember to follow best practices and prioritize security in your contracts.

With patience and practice, you'll be well on your way to becoming a proficient Solidity developer.

Happy coding!

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