Elixir GenServer Error Fix

The Hook

You will learn how to fix common otp gen server errors. This matters because understanding this concept is essential for productive development. Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro.

Quick Fix

GenServer

The wrong approach and the correct fix are shown below:

Wrong:

defmodule Counter do
  use GenServer
  def start_link(initial) do
    GenServer.start_link(__MODULE__, initial)
  end
  def init(state), do: {:ok, state}
end

Output:

Right:

defmodule Counter do
  use GenServer
  def start_link(initial) do
    GenServer.start_link(__MODULE__, initial, name: __MODULE__)
  end
  def init(state), do: {:ok, state}
  def inc(pid), do: GenServer.cast(pid, :inc)
  def value(pid), do: GenServer.call(pid, :value)
  def handle_call(:value, _from, state), do: {:reply, state, state}
  def handle_cast(:inc, state), do: {:noreply, state + 1}
end

Output:

Prevention

GenServer: client-server pattern. call: synchronous with reply. cast: async, no reply.

Common Mistakes with otp gen server

1. Non-exhaustive pattern matches that compile with warnings then crash at runtime
2. Misunderstanding that String is [Char] with poor performance for large text operations
3. Using foldl instead of foldl' causing stack overflow on large lists

These mistakes appear frequently in real-world ELIXIR code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ