Equality and identity in Dart

I am just starting to study Dart and a question arose, a clear answer to which I could not find or formulate for myself. I'm trying to figure out the difference between == and identity(). Using the example of this code snippet:

void main() {
  var a = [1, 2, 3];
  var b = a;
  var c = [1, 2, 3];

  print(identical(a, b)); // true
  print(identical(a, c)); // false
  print(a == c);  // false
}

I have a little experience in python and there this code gives me understandable results:

>>> a = [1, 2, 3]
>>> b = [1, 2, 3]
>>> a == b
True
>>> a is b
False

And in Dart it is not clear for me. If identity and == on basic data types give the same results, then why are they different 😅 ? Is there a difference between them if I'm not familiar with the classes in Dart?

I will be grateful for any clarifications that will help me figure out the issue.

Solution

The example below might help to illustrate the usage of the operator == and the function identical.

By default, == and identical return the same result. See first example, where two objects of type A are compared. The hashCode can be thought of as an object id. Note: Classes may override the == operator and the getter hashCode. For this reason it makes sense to have the function identical which is the equivalent of Python's is.
The second example is slightly different since both variables s1 and s2 are assigned a literal, in this case a String literal. (To achieve a similar behaviour with class A, we could define a const constructor and use that constructor when assigning the values of a1 and a2.)
The third example is similar to the second one. In this case, l1 and l2 are both assigned the same constant list object.
The forth example shows that (non-constant) collections (lists, sets, maps, etc) are only equal == if they are also identical, even if their elements are the same.

class A{}

void main() {
  
  print('\nClass A');
  final a1 = A();
  final a2 = A();
  print(a1 == a2); // false
  print(identical(a1, a2)); // false
  print(a1.hashCode);
  print(a2.hashCode);
  
  print('\nString');
  final s1 = 'hi'; 
  final s2 = 'hi';
  print(s1 == s2); // true
  print(identical(s1, s2)); // true
  print(s1.hashCode);
  print(s2.hashCode);
  
  print('\nConst list');
  final l1 = const [0, 1, 2]; 
  final l2 = const [0, 1, 2]; 
  print(l1 == l2); // true
  print(identical(l1, l2)); // true
  print(l1.hashCode);
  print(l2.hashCode);
  
  print('\nList');
  final l3 = [0, 1, 2]; 
  final l4 = [0, 1, 2]; 
  print(l3 == l4); // false
  print(identical(l3, l4)); // false
  print(l3.hashCode);
  print(l4.hashCode);
}

The console output is shown below:

Class A
false
false
945090685
653872300

String
true
true
793667904
793667904

Const list
true
true
996765025
996765025

List
false
false
61814395
515290226