Why does the identityHashCode function not work for the built-in type 'int' in Dart? - flutter

Question

The documentation of the identityHashCode says:
And it indeed works for my custom type 'Integer':
class Integer {
int num;
Integer(this.num);
#override
int get hashCode {
return num;
}
#override
bool operator ==(Object other) {
if(other is Integer && this.num == other.num) {
return true;
}
return false;
}
}
void main() {
Integer n1 = Integer(1);
print(n1.hashCode); // print "1"
print(identityHashCode(n1)); // print "650939380", a different value!
}
But for the built-in type 'int', identityHashCode(int) seems to always return the same value as int.hashCode, which is the numerical value itself:
void main() {
int n = 1;
print(n.hashCode); // print "1"
print(identityHashCode(n)); // still print "1", the same value as n.hashCode!
}
Anyone know why this is happening? I'm confused now.😵

Answer 1

int is Built-in type (not a usual class)
In documentation identityHashCode has a note:
This hash code is compatible with [identical], which just means that
it's guaranteed to be stable over time.
For compiler all int values are constants. identical for the same constants shows true. So hashCode of int was made by own value (which also int).
print(identical(1, 1)); // true
According to this comment int (and double) has own condition for comparing in identical function.
By the same numeric value
Here's some code for example representation:
void main() {
int a = 1; // '1' is a constant
int b = 1;
int c = 2; // '2' is a constant
print(identical(a, b)); // true
print(identical(a, c)); // false
print(identical(1, 1)); // true
print(identical(1, 2)); // false <= 1 and 2 are constants
print(identical(a, 1)); // true
print(identical(c, 1)); // false
print(identical(c, 2)); // true
print(identityHashCode(a)); // 1
print(identityHashCode(b)); // 1
print(identityHashCode(c)); // 2
print(identityHashCode(1)); // 1
print(identityHashCode(2)); // 2
}