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no-wildcard-variable-uses

Same as no_wildcard_variable_uses in Dart lints

Path
lint/suspicious/no-wildcard-variable-uses
Default
On (recommended)
Origin
Dart lints
Rule
298 of 512
recommended

Flags references to a wildcard variable or parameter (a name made solely of underscores, such as _ or __).

An all-underscore name marks a binding as intentionally unused, and under Dart's wildcard-variable semantics such names are non-binding — reading one back does not retrieve the value you expect. Referencing it is therefore either a mistake or a reliance on behavior that is changing. Declaring a wildcard is fine; only uses in expression position are reported. Give the binding a real name if you actually need its value.

Invalid

example.dartdart
// Referencing a wildcard variable or parameter is not allowed.

int a(int _) => _;

int b(int _) => _ * 2;

void c() {
  var _ = 1;
  print(_);
}

void d() {
  var __ = 2;
  print(__);
}

int e(int _) {
  return _ + 1;
}

void f() {
  var _ = 0;
  _ = 5;
}
Don't use a wildcard parameter or variable.
2
3int a(int _) => _;
Don't use a wildcard parameter or variable.
4
5int b(int _) => _ * 2;
Don't use a wildcard parameter or variable.
8 var _ = 1;
9 print(_);
Don't use a wildcard parameter or variable.
13 var __ = 2;
14 print(__);
Don't use a wildcard parameter or variable.
17int e(int _) {
18 return _ + 1;
Don't use a wildcard parameter or variable.
22 var _ = 0;
23 _ = 5;

Valid

example.dartdart
// Wildcards may be declared but never referenced.

void a() {
  var x = 1;
  print(x);
}

int b(int value) => value;

void c(int _) {}

void d() {
  var _ = 1;
}

void e() {
  [1, 2].forEach((_) {});
}

void f() {
  for (var _ in <int>[]) {}
}

Configure no-wildcard-variable-uses

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

falcon.jsonjson
{
  "linter": {
    "rules": {
      "suspicious": {
        "no-wildcard-variable-uses": "error"
      }
    }
  }
}

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

example.dartdart
// falcon-ignore lint/suspicious/no-wildcard-variable-uses: <reason>