Pattern

class Locator {
  static final Locator I = Locator._();
  Locator._();

  late ApiClient api;

  static T get<T>() {
    if (T == ApiClient) return I.api as T;
    throw StateError('unknown $T');
  }
}

void sendPing() {
  final client = Locator.get<ApiClient>();
  client.post('/ping', body: null);
}

Problems

• Call sites hide dependencies; you cannot see ApiClient from the signature.
• Tests must mutate global registry order; parallel tests race.
• Refactors miss call sites because there is no constructor to update.

Better direction

• Pass ApiClient into sendPing or into a class that owns sendPing.
• Use a container only at the edge (main) and inject concrete dependencies inward.

Practice tasks

• Find one getIt<...>() (or similar) inside a domain class and move the type to a constructor parameter.
• List three test failures you have seen from “forgot to register mock in locator.”
• Compare pure constructor injection vs container resolves graph in two sentences for your team wiki.