falcon

Rules / Style / prefer-iterable-where-type

prefer-iterable-where-type

lint/style/prefer-iterable-where-type
recommended
Same as prefer_iterable_whereType · Dart lints

Flags .where((e) => e is T), which .whereType<T>() expresses directly.

Filtering an iterable with an is test is exactly what Iterable.whereType does, but the getter also narrows the element type, yielding an Iterable<T> instead of leaving the original element type in place. Using whereType<T>() is shorter, avoids the throwaway closure, and removes the casts or checks that a bare where filter would still require downstream. The rule matches a single-argument .where call whose sole positional argument is a one-parameter arrow closure of the form param is T — the test must be non-negated and applied to the closure's own parameter.

Invalid

example.dartdart
void bad() {
  var a = items.where((e) => e is String);
  var b = list.where((x) => x is int);
  var c = things.where((t) => t is Widget);
  var d = values.where((v) => v is double).toList();
  var e = data.where((item) => item is Map);
}
Use 'whereType<T>()' instead of 'where' with an 'is' check.
1void bad() {
2 var a = items.where((e) => e is String);
Use 'whereType<T>()' instead of 'where' with an 'is' check.
2 var a = items.where((e) => e is String);
3 var b = list.where((x) => x is int);
Use 'whereType<T>()' instead of 'where' with an 'is' check.
3 var b = list.where((x) => x is int);
4 var c = things.where((t) => t is Widget);
Use 'whereType<T>()' instead of 'where' with an 'is' check.
4 var c = things.where((t) => t is Widget);
5 var d = values.where((v) => v is double).toList();
Use 'whereType<T>()' instead of 'where' with an 'is' check.
5 var d = values.where((v) => v is double).toList();
6 var e = data.where((item) => item is Map);

Valid

example.dartdart
void good() {
  var a = items.whereType<String>();
  var b = list.where((e) => e.isValid);
  var c = things.where((e) => e is! String);
  var d = values.where((e) => e is int && e > 0);
  var e = data.where((a, b) => a is int);
  var f = items.map((e) => e is String);
}

How to configure

Set the severity of prefer-iterable-where-type in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-iterable-where-type": "error"
      }
    }
  }
}

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