prefer_add_all

v0.8.0 Warning Fix Collection Type

This rule flags two ways of adding elements one at a time: a for-in loop whose only statement adds the loop variable, and several consecutive add calls on the same collection.

Why use this rule

for (final x in source) target.add(x); is target.addAll(source) spelled out across three lines. The loop form makes the reader decode control flow to recognise a single operation, and it hides the intent from anyone skimming.

The same applies to target.add(a); target.add(b); — one addAll([a, b]) states the intent in a single call.

addAll is also free to be more efficient — a List can grow its backing store once instead of on each add.

Don’t

for (final item in newItems) {
  selected.add(item);
}

selected.add('first');
selected.add('second');

Do

selected.addAll(newItems);

selected.addAll(['first', 'second']);

Known limitations

For the loop form, only the exact copy pattern is reported. The rule stays silent whenever the loop does anything else:

• The added value is not the loop variable unchanged — target.add(x.name) is a map, not a copy.
• The body has more than one statement, or wraps the add in a condition.
• The loop is indexed (for (var i = 0; ...)) rather than for-in, since it may skip or reorder elements.
• The method is anything other than add.

For consecutive calls, a run is broken by any other statement, so add(a); log(); add(b); is left alone. The receiver must also be a plain variable or property chain — items[i].add(x) may denote a different object on each call — and it must be a collection, since add exists on many unrelated types.

Configuration

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name.

To turn it off:

many_lints.yaml

rules:
  prefer_add_all: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• list_all_equatable_fields — Ensure all fields are listed in Equatable props.
• avoid_accessing_collections_by_constant_index — Avoid accessing a collection by a constant index inside a loop.
• avoid_collection_equality_checks — Avoid comparing collections with == or != as it checks reference equality, not contents.
• avoid_collection_methods_with_unrelated_types — Avoid calling collection methods with arguments whose types are unrelated to the collection’s type parameter.