Events & Logs — Kudos board build (step 2/6)

GoalAdd per-user storage so everyone can leave a personalized kudos.

Cryptography is about how to maintain control over information.

— Shafi Goldwasser

What to write

1. Mapping
   declare mapping(address => string) private _lastKudos;.
   Copy

   mapping(address => string) private _lastKudos;

   Mappings give O(1) lookups keyed by address and grow only when written.

2. Setter
   store a message for a recipient.
   Copy

   function setKudos(address to, string calldata message) external {
       _lastKudos[to] = message;
   }

   External + calldata keeps the ABI lean and avoids memory copies.

3. Getter
   read the latest kudos for an address.
   Copy

   function lastKudos(address user) external view returns (string memory) {
       return _lastKudos[user];
   }

   View reads are free off-chain and return a memory copy of stored data.

Why Mappings scale per-user; a focused setter/getter keeps the ABI minimal.

Try it Deploy, call setKudos(to, message), then lastKudos(to) to confirm storage.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract KudosBoard {
    mapping(address => string) private _lastKudos;

    function setKudos(address to, string calldata message) external {
        _lastKudos[to] = message;
    }

    function lastKudos(address user) external view returns (string memory) {
        return _lastKudos[user];
    }
}

NextWe’ll keep extending this in the following lesson; this version already deploys and runs.