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prefer-typing-uninitialized-variables

Same as prefer_typing_uninitialized_variables in Dart lints

Group
Style
Path
lint/style/prefer-typing-uninitialized-variables
Default
On (recommended)
Origin
Dart lints
Rule
414 of 512
recommended

Flags uninitialized variables declared without a type annotation.

When a declaration has no initializer, there is no value for the analyzer to infer a type from, so var x; leaves the variable as dynamic — silently opting out of static checking on every later use. Writing int x; instead documents intent and restores type safety at no cost. The rule fires only on declarators that are both untyped and uninitialized; a declaration is exempt as soon as it carries a type annotation. It covers local variables, fields, and top-level variables.

Invalid

example.dartdart
// Uninitialized variables without a type annotation.
var topLevel;

void f() {
  var a;
  var b;
  late var d;
  a = 1;
  b = 2;
  d = 3;
  print(a + b + d);
}

class C {
  var field;
  static var s;
}
Prefer typing uninitialized variables and fields.
1// Uninitialized variables without a type annotation.
2var topLevel;
Prefer typing uninitialized variables and fields.
4void f() {
5 var a;
Prefer typing uninitialized variables and fields.
5 var a;
6 var b;
Prefer typing uninitialized variables and fields.
6 var b;
7 late var d;
Prefer typing uninitialized variables and fields.
14class C {
15 var field;
Prefer typing uninitialized variables and fields.
15 var field;
16 static var s;

Valid

example.dartdart
// Either a type annotation or an initializer is present.
int topLevel = 0;

void f() {
  int a;
  var b = 1;
  final c = 2;
  String? d;
  double e = 0.0;
  a = 5;
  d = 'x';
  print(b + c + e + a + d.length);
}

class C {
  int field = 0;
  var typed = 'x';
  static int s = 1;
}

Configure prefer-typing-uninitialized-variables

Set its severity in falcon.json. See the configuration guide.

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-typing-uninitialized-variables": "error"
      }
    }
  }
}

Or silence one occurrence with a suppression comment; the reason is required.

example.dartdart
// falcon-ignore lint/style/prefer-typing-uninitialized-variables: <reason>