Data classes | Kotlin

The compiler automatically derives the following members from all properties declared in the primary constructor:

• .equals()/.hashCode() pair.
• .toString() of the form "User(name=John, age=42)".
• .componentN() functions corresponding to the properties in their order of declaration.
• .copy() function (see below).

To ensure consistency and meaningful behavior of the generated code, data classes have to fulfill the following requirements:

• The primary constructor must have at least one parameter.
• All primary constructor parameters must be marked as val or var.
• Data classes can't be abstract, open, sealed, or inner.