What is an Enum?

The word Enum stands for Enumerable. These are value types that consist of a predefined list of constant values. The values in the enumerated list are called enums and they remain constants. In solidity, enums are the only way to create a user-defined type.

Enums Use Cases

• Optional/nullable data type

• Flag with extra information needed in some cases -Variant data types

• Modeling states in a state machine where each stale can have some data associated with it. -List of operators for batching processing where each operation can have its own argument

• Alternative function overloading that makes avoiding combinatorial explosion when there are multiple parameters that need variants

• Nested data structures with heterogeneous nodes.

What can’t be done with Enums

• Implicit conversations

• Adding numbers or booleans as members of the enums

• Using Enums as key type mapping

• Defining enums in solidity with a compiler version lower than 0.5.0

• Enums cannot be declared within functions

Plain Enum:

Enum Alphabets{A, B, C}

Declaring An Enum

//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

contract EnumExample {
    // creates an enum 
    Enum Zipper{Up, Down}

    //Declares the variable of the type Zipper
    Zipper public zipper;

    // First Function to take up zipper
    function zipperUp() public {
        zipper = Zipper.Up;
    }

     // Second Function to bring down zipper
    function zipperDown() public {
        zipper = Zipper.Down;
    }

    //Function to get the value of zipper;
    function getZipperState() public view returns(Zipper){
        return zipper;
    }
}