The hash value of the value, which allows the value to be an element of a hash-based set or key of a hash-based map. Implementations must respect the constraint that:

• if x==y then x.hash==y.hash.

Therefore, a class which refines equals must also refine hash.

A developer-friendly string representing the instance. Concatenates the name of the concrete class of the instance with the hash of the instance. Subclasses are encouraged to refine this implementation to produce a more meaningful representation.

Compares this value with the given value. Implementations must respect the constraints that:

• x==y if and only if x<=>y == equal (consistency with equals()),
• if x>y then y<x (symmetry), and
• if x>y and y>z then x>z (transitivity).

Determine if two values are equal. Implementations should respect the constraints that:

• if x===y then x==y (reflexivity),
• if x==y then y==x (symmetry),
• if x==y and y==z then x==z (transitivity).

Furthermore it is recommended that implementations ensure that if x==y then x and y have the same concrete class.

A class which explicitly refines equals() is said to support value equality, and the equality operator == is considered much more meaningful for such classes than for a class which simply inherits the default implementation of identity equality from Identifiable.

The result of adding the given value to this value. This operation should never perform any kind of mutation upon either the receiving value or the argument value.