In Kotlin there are two types of equality:
- Referential equality (two references point to the same object);
- Structural equality (a check for
Referential equality is checked by the
=== operation (and its negated counterpart
a === b evaluates to
true if and only if
b point to the same object.
Structural equality is checked by the
== operation (and its negated counterpart
!=). By convention, an expression like
a == b is translated to:
a?.equals(b) ?: (b === null)
a is not
null, it calls the
equals(Any?) function, otherwise (i.e.
null) it checks that
b is referentially equal to
Note that there's no point in optimizing your code when comparing to
a == null will be automatically translated to
a === null.
Floating point numbers equality
When an equality check operands are statically known to be
Double (nullable or not), the check follows the IEEE 754
Standard for Floating-Point Arithmetic.
Otherwise, the structural equality is used, which disagrees with the standard so that
NaN is equal to itself, and
-0.0 is not equal to