yuri_notes.md

Class Notes for Yuri Oliveira

Book: Designing Elixir Systems with OTP

Do      -> Data       \
Fun     -> Functions   -> Core is a place for certainty
Things  -> Tests      /
With
Big     -> Boundaries             \
Loud    -> Lifecycles              -> Encapsulates uncertainty, protects the Core
Worker  -> Workers / Dependencies /
Bees

On Data and Functions

• Constructors -> initiate state (?)
• Reducers -> takes an accumulator and returns the transformed accumulator (of the same type)
• Converters/Transformers

On API

• Backpressure: slowing down the client requests to avoid overwhelming the server due to how fast it is to pass messages around

---

Notes from OTP Module

Tasks and Agents

• Agents tracks running state (GenServer)

> {:ok, agent} = Agent.start_link(fn -> 0 end)
{:ok, #PID<0.128.0>}
iex(11)> Agent.get(agent, fn x -> x end)
0
iex(12)> Agent.get(agent, fn x -> x+1 end)
1
iex(14)> Agent.get(agent, & &1)
0
iex(15)> Agent.get(agent, & &1+1)
1
iex(18)> Agent.update(agent, &(&1+1))
:ok

Tasks

• Are "run and forget", but can await
• You loose control
• Task.await/2 has a default timeout of 5000

> long_work = fn -> Process.sleep(4000); 42 end

> task = Task.async(long_work)

> 1+ Task.await(task)

> Process.alive? task.pid

Do not use structs around the params and the boundary, don't expose internal data