Singleton

Singleton: one shared instance for the whole app

Problem: you want exactly one instance of something — a Config, a shared Stripe client, a logger — and one global point to reach it.

PawWalk scenario: app configuration loaded once at boot. Every part of the API reads the same Config object; nobody should build a second one.

Ruby ships the pattern in the stdlib: require "singleton"; include Singleton makes .new private and gives you .instance.

Be honest: in Ruby a plain constant or a module of module-methods is usually enough. Reach for Singleton only when you need lazy init plus a real object with state.