falcon

Rules / Style / prefer-generic-function-type-aliases

prefer-generic-function-type-aliases

lint/style/prefer-generic-function-type-aliases
recommended
Same as prefer_generic_function_type_aliases · Dart lints

Flags old-style function typedefs written with inline parameter syntax.

Dart's original typedef form, typedef int F(int x);, predates generic function types and cannot express a function type in every position the modern syntax can. Rewriting it as typedef F = int Function(int); is more uniform, composes with generics, and reads consistently with other type aliases. Because the parser only accepts the modern typedef Name = Type; form, detection scans the raw source rather than the AST: a typedef whose declaration reaches an opening ( before any = or ; is the old, non-generic form. The scan skips comments and string literals so the keyword appearing in text is not mistaken for a declaration.

Invalid

example.dartdart
// Old-style (non-generic) function typedefs.
typedef int Compare(int a, int b);
typedef void Callback(String msg);
typedef bool Predicate(Object o);
typedef String Formatter(int value);
typedef num Reducer(num a, num b);
typedef void Handler();
Use the generic function type syntax in typedefs.
1// Old-style (non-generic) function typedefs.
2typedef int Compare(int a, int b);
Use the generic function type syntax in typedefs.
2typedef int Compare(int a, int b);
3typedef void Callback(String msg);
Use the generic function type syntax in typedefs.
3typedef void Callback(String msg);
4typedef bool Predicate(Object o);
Use the generic function type syntax in typedefs.
4typedef bool Predicate(Object o);
5typedef String Formatter(int value);
Use the generic function type syntax in typedefs.
5typedef String Formatter(int value);
6typedef num Reducer(num a, num b);
Use the generic function type syntax in typedefs.
6typedef num Reducer(num a, num b);
7typedef void Handler();

Valid

example.dartdart
// Modern generic function type syntax, plus non-function aliases.
typedef Compare = int Function(int a, int b);
typedef Callback = void Function(String msg);
typedef Predicate<T> = bool Function(T value);
typedef IntList = List<int>;
typedef Json = Map<String, dynamic>;
typedef VoidFn = void Function();

How to configure

Set the severity of prefer-generic-function-type-aliases in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-generic-function-type-aliases": "error"
      }
    }
  }
}

Related