var_with_no_type_annotation

Avoid declaring parameters with var and no type annotation.

NOTE: This rule is removed in Dart 3.13.0; it is no longer functional.

The analyzer produces this diagnostic when a parameter is declared using the keyword var without a type annotation.

This pattern should be avoided as it likely will be a compile-time error in a future version of Dart. Beyond this, using var without an explicit type results in the parameter having a type of dynamic, disabling static type checking for that parameter.

The following code produces this diagnostic because the parameter x is declared with var:

// @dart=3.12
void f(var x) {
  print(x);
}

The following code produces this diagnostic because the initializing formal parameter x is declared with var:

// @dart=3.12
class C {
  int x;
​
  C(var this.x);
}

If you know the desired type of the parameter, then replace var with a type annotation:

void f(String x) {
  print(x);
}

If you don't know or don't want any specific type for the parameter, then replace var with a type of Object? or dynamic to make the lack of any more specific type explicit:

void f(Object? x) {
  print(x);
}