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

Question

Say I have a class that has many instance variables,. I want to overload the == operator (and hashCode) so I can use instances as keys in maps.

class Foo {   int a;   int b;   SomeClass c;   SomeOtherClass d;   // etc.    bool operator==(Foo other) {     // Long calculation involving a, b, c, d etc.   } } 

The comparison calculation may be expensive, so I want to check if other is the same instance as this before making that calculation.

How do I invoke the == operator provided by the Object class to do this ?

Answer 1

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 } 

Answer 2

You can use identical(this, other).