Build a key-value store
Concept pages show one idea at a time. Real programs combine them, so each track ends with a project that does exactly that. Across the whole site we build one program and keep growing it: KV, a small key-value store.
Why a key-value store?
It's the smallest program that touches everything Elixir is good at. A store needs a data structure and an API (this track), then has to be shared by many callers at once and survive crashes (the OTP track), and finally has to live on more than one machine (the Distributed track). Caches, session stores, rate limiters and service registries are all KV stores underneath.
What changes along the way
| Track | The store is… | You'll use |
|---|---|---|
| Core Elixir (this chapter) | an immutable value passed around by functions | maps, modules, structs, with, protocols |
| Processes and OTP | a supervised process, with fast reads and expiring keys | GenServer, supervisors, Registry, ETS, timers |
| Distributed Elixir | replicated across nodes | nodes, :global, :pg (Mnesia and partitions coming) |
How the steps work
Each step is one runnable file that stands on its own: it redefines what it needs instead of importing earlier steps, so you can open any step and run it. Every step says what changed since the last one and which problem the next one solves. The concept pages each step builds on are linked at the top.
Before you start
The steps build on MapsModules and Named FunctionsStructswithErrors and Tagged TuplesEnumThe Pipe OperatorProtocols
Steps
- A map is already a store Across these steps we build KV, a small key-value store, and keep growing it: concurrent, supervised, cached in ETS, expiring keys, and later distributed acr...
- Give it a proper type Step 1's store was a bare map, so nothing stopped a caller from passing any map, or storing keys we never meant to allow. This step gives KV its own type: a ...
- Many buckets One flat namespace gets crowded. Step 3 groups keys into named buckets (a map of maps) and adds a protocol so the store can be exported to a simple text form...