learn.dart+flutter shafi.dev

← → or space · progress saves for Continue on the roadmap

Goal

Split “God classes” that mix unrelated reasons to change.

Symptoms

  • One file imports UI, HTTP, SQL, and business rules.
  • Changing validation forces retesting persistence code.
  • Class name is vague (Manager, Helper, Util) and the file is huge.

Refactor moves

  • Extract persistence (repository), rules (domain service), DTO mapping, and transport (HTTP handlers) into separate types.
  • Keep each extracted type named after its job (UserValidator, UserRepository).

Dart angle

  • lib/services/user_service.dart orchestrates; it should not open sockets directly if you can pass a UserRepository.

Practice tasks

  • Open your largest class and list three distinct “reasons to change”; sketch three target types.
  • Move one pure function (no I/O) to a dedicated library file and import it from the service.
  • Delete dead branches uncovered after the split (merge artifacts).