LinkedHashMap is unable to find an existing key

[rebaz94]

I've come across a bug in the map where the key exists in the map, but it can't be found.

final LinkedHashMap<String, dynamic> data = LinkedHashMap.identity();
print(data['key1']); // returns null
print(data.containsKey('key1')); // returns false
print(data.keys.contains(id)); // returns true

In this example, despite 'key1' being present in the map but it return null, and containsKey incorrectly reports its absence. However, when checking the map's entries, using keys or checking with == equality return the value

Screen.Recording.2024-05-14.at.9.33.53.PM.mp4

[lrhn]

Edit: Ah, it was a movie, not a picture. Makes more sense now.

That does look suspicious, almost as if the hash table has been built using the wrong hash numbers.
(That said, a Map's keys.contains should work exactly the same as containsKey, so getting a different result is itself a sign of something not being correct. Quoting the keys documentation:

The returned iterable has efficient length and contains operations, based on length and containsKey of the map.

So something is off.)

[rebaz94]

sorry for bad example, This code snippet just an example how I utilized the map. please check the video

final LinkedHashMap<String, dynamic> data = LinkedHashMap.identity();
print(data['key1']); // returns null
print(data.containsKey('key1')); // returns false
print(data.keys.contains(id)); // returns true

[mraleph]

@rebaz94 Dart does not require String instances to be globally canonicalized (with some exceptions around compile time constants). This means two strings can be equal but not identical (because they are represented by different objects).

Simple example:

void main() {
  final s0 = 'key1';
  final s1 = 'key1,key2'.split(',').first;
  print(s0 == s1);
  print(identical(s0, s1));
}

This means using LinkedHashMap<String, ...>.identity() is not a good idea (it is a map which uses key identity rather than equality) unless you somehow ensure canonicalization (e.g. you have another Map<String, String> somewhere which stores canonical instances).

[rebaz94]

Ah, got it. Thank you for the clarification.

[lrhn]

I'm still worried that .keys.contains does not answer the same as .containsKey. That suggests that .keys.contains is probably also not efficient. The documentation for keys states that it must have efficient contains (fx. backed by the map's containsKey.)