avoid-global-state-and-init

Summary

Avoid using package-level variables (Globals) for application state (like Database connections, Configs, Loggers) and avoid init() functions for side-effects. Instead, use Dependency Injection: pass dependencies explicitly to your structs or functions (controllers/handlers).

Rationale

• Traceability: It is clear what a component depends on by looking at its constructor or fields.
• Testability: Globals make parallel testing impossible (race conditions) and mocking difficult. You cannot run two tests with different configurations if they share a global config variable.
• Order of Initialization: init() execution order can be subtle and hard to debug. Explicit wiring (main.go) is predictable.

Guidance

1. No var db *sql.DB at package level.
2. No func init() { config.Load() }.
3. Pattern:
   • Define a struct that holds dependencies.
   • Create a "Constructor" (Factory) function.
   • Wire everything in main.go.

Examples