How do I compare two objects to see if they are the same instance, in Dart?

For completeness, this is a supplemental answer to the existing answers.

If some class Foo does not override ==, then the default implementation is to return whether they are the same object. The documentation states:

The default behavior for all Objects is to return true if and only if this object and other are the same object.

You can use identical(this, other).

You're looking for "identical", which will check if 2 instances are the same.

identical(this, other);

A more detailed example?

class Person {
  String ssn;
  String name;

  Person(this.ssn, this.name);

  // Define that two persons are equal if their SSNs are equal
  bool operator ==(Person other) {
    return (other.ssn == ssn);
  }
}

main() {
  var bob = new Person('111', 'Bob');
  var robert = new Person('111', 'Robert');

  print(bob == robert); // true

  print(identical(bob, robert)); // false, because these are two different instances
}