`LinkedHashMap<String, T>();` is changed to `<String, T>{};` after `dart fix`

[tolotrasamuel]

LinkedHashMap<String, T>(); is changed to <String, T>{}; after dart fix

class CollectionState<K, T> {
  final LinkedHashMap<String, T> data;
  final Map<String, List<String>> subsetState;

  CollectionState({
    LinkedHashMap<String, T>? data,
    this.subsetState = const {},
  }) : data = data ?? LinkedHashMap<String, T>();

}

Map is not the same as LinkedHashMap.

[dart-github-bot]

Summary: dart fix incorrectly converts LinkedHashMap<String, T>() to <String, T>{}, losing the LinkedHashMap's insertion order. This breaks code relying on LinkedHashMap's specific behavior.

[lrhn]

It's not typed the same, but {} really is a LinkedHashMap.

The fix shouldn't break your typed code.
On the other hand, your typed code is should use Map<String, T> for the variable type. There is never any good reason to use LinkedHashMap as a type - it has the same API as Map.

[tolotrasamuel]

Okay. I guess I was confused by the documentation. https://api.dart.dev/dart-core/Map-class.html

Maps, and their keys and values, can be iterated. The order of iteration is defined by the individual type of map. Examples:

The plain HashMap is unordered (no order is guaranteed),
the LinkedHashMap iterates in key insertion order,
and a sorted map like SplayTreeMap iterates the keys in sorted order.

The above does not directly suggested that the default implementation of Map is LinkedHashMap.

After reading your responses, that only when I saw down the page:

Map()
Creates an empty LinkedHashMap.
factory

Maybe it will help to put that statement in the documentation text section.

[rakudrama]

It is definitely a bug if dart fix causes your program to no longer compile.

While the documentation for Map() and LinkedHashMap do mention the map literal syntax {}, it does not explain that the map literal syntax has static type Map but, for non-const map literals, is implemented by LinkedHashMap.

There is never any good reason to use LinkedHashMap as a type - it has the same API as Map.

Nitpick: I disagree with 'never' here. I would say 'usually no reason'.

LinkedHashMap guarantees to maintain the insertion order, something which is cannot be expressed other than by using the type explicitly. This might be important to the algorithms that use data.

I always use the type Map and a map literal {} unless I care about the insertion order, which is almost never.
Over the years we have put a lot of effort into making the default Map be the best Map for most uses.

[tolotrasamuel]

I agree. dart fix should "fix" the code, not cause a compile time error.