_Follow along with this video:_ --- ### Storage Refresher With our function dispatcher and interfaces set up, we're finally ready to add some logic to our macros! We're going to begin with `SET_NUMBER_OF_HORSES()` as one of our first steps will be assigning a storage slot to our `numberOfHorses` variable. When we think of storage, we can think of it as a giant, persistent array. When a transaction's execution completes, storage remains and is not cleared. In Solidity each variable is mapped to a storage slot sequentially as they are defined in the contract. It's important to note however: - Constant Variables are not saved to storage - Mappings and arrays are handled uniquely using a hashing algorithm to assign the storage locations of their contents. Specific details on this can be found in the [**Ethereum Documentation**](https://docs.soliditylang.org/en/latest/internals/layout_in_storage.html). - Memory variables are not saved to storage So, in order to update storage, there are a few things we need to do. ```js #define macro SET_NUMBER_OF_HORSES() = takes(0) returns(0){ // 1. Give numberOfHorses a storage slot // 2. Get the value to store from call data // 3. Execute the SSTORE op code } ``` Great! Once we've implemented this logic, we're going to be able to write some tests to compare the functionality of our Huff contract with that of our Solidity version, and - hopefully - we'll see they do exactly the same thing. Let's go!