What are enums in Solidity?

enums or members of enumerated lists, in Solidity work much like enums in any other language. For me, it is basically a tool to reduce the stress on my mental RAM while writing code or smart contracts.

Typical Use Case:

Suppose you want to give your user an option to choose his favorite squad among 9 available options. The available options would be:

Black Bull
Silver Eagle
Blue Rose
Golden Dawn
Green Mantis
Crimson Lion
Aqua Deer
Purple Orca
Coral Peacock

Suppose you intend to use the variable favSquad to denote your user’s favorite Black Clover squad and use that variable in subsequent logic.

One option (particularly messy one) would be to allow users to enter strings that denote their favorite squads, but that would bring forth a whole new hell of matching proper cases (upper cases and lower cases), also someone could enter a string that is out of scope, like Spade Kingdom for example.

Another option would be to assign numbers to each squad (0-8) based on their index, most probably like a mapping. That would work, but you’ll have to always remember which number represents which squad while coding, which would be pretty uncomfortable.

Hence, we pivot towards using enums. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums. With the use of enums it is possible to reduce the number of bugs in your code. This helps you to not make a mistake, to enter something out of the domain, while entering data and also improves the program readability.

For example, this is how we would use enums:

pragma solidity ^ 0.8.0;

contract testEnums {
  enum CloverSquad {
    BlackBull,
    GoldenDawn,
    SilverEagle,
    BlueRose,
    CrimsonLion,
    GreenMantis,
    CoralPeacock,
    PurpleOrca,
    AquaDeer
  }
  
  CloverSquad favSquad;
  CloverSquad firstRankedSquad = CloverSquad.GoldenDawn;
  
  function getFirstRankedSquad() public view returns (CloverSquad) {
    return firstRandkedSquad;
  }
}

Taking enum inputs and checking invalid inputs

A question that might arise in your minds (it did in mine too 😅) is how do we take enums as input from the user of our smart contract. We do this by typecasting the enums and checking if it is out of range or not.

Example:

// Yes, you can use your enums in mappings.
mapping (address => CloverSquad) public playerSquad;

function selectFavoriteSquad(uint userFavSquad) external {
  require(userFavSquad <= uint(CloverSquads.AquaDeer), "Choose from 0 to 8");
  playerSquad[msg.sender] = CloverSquad(userFavSquad);
  // Further Logic....
}

solidity-nirvana

A collection of short blogs, explanations and walk-throughs about common Solidity practices, problems and patterns

What are enums in Solidity?

Typical Use Case:

Taking enum inputs and checking invalid inputs

Further Reading