avoid_generics_shadowing

v0.4.0 Warning Fix Code Organization

Flags generic type parameters that shadow a top-level type declaration (class, mixin, enum, typedef, or extension type) in the same file. When a type parameter has the same name as a real class, it becomes confusing whether a reference points to the generic or the concrete type.

Why use this rule

Shadowing a top-level type with a generic parameter silently replaces the concrete type with an unbounded generic within that scope. This can lead to subtle bugs where code appears to reference a specific class but actually operates on an unrelated type parameter. Using conventional single-letter names like T, R, or E eliminates the ambiguity.

See also: Dart language - Generics | Dart lint: avoid_shadowing_type_parameters

Don’t

class MyModel {}
enum MyEnum { first, second }

// Generic type parameter shadows the top-level class MyModel
class Repository<MyModel> {
  MyModel get(int id) => throw '';
}

class SomeClass {
  // MyEnum shadows the top-level enum
  void method<MyEnum>(MyEnum p) {}
}

// Both type parameters shadow top-level types
class BadPair<MyModel, AnotherClass> {
  final MyModel first;
  final AnotherClass second;
  BadPair(this.first, this.second);
}

Do

class MyModel {}
enum MyEnum { first, second }

// Use conventional single-letter type parameters
class GoodRepository<T> {
  T get(int id) => throw '';
}

// Descriptive names that don't shadow top-level types
class GoodPair<TFirst, TSecond> {
  final TFirst first;
  final TSecond second;
  GoodPair(this.first, this.second);
}

class Processor {
  void process<T>(T item) {}
  R transform<R>(Object input) => throw '';
}

Configuration

This rule is in the recommended preset, so it is on with preset: recommended or preset: opinionated. Add it to preset: core with avoid_generics_shadowing: true.

To turn it off:

many_lints.yaml

rules:
  avoid_generics_shadowing: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• arguments_ordering — Keep named arguments in a configured order.
• avoid_duplicate_mixins — Flag a mixin applied twice in one with clause.
• avoid_unnecessary_constructor — Remove a constructor identical to the default one.
• avoid_unnecessary_extends — Remove an explicit extends Object.