Data classes are primarily used to hold data in Kotlin. They are marked with the keyword data.

data class Item (
	val id: Int = 0,
	val itemName: String,
	val itemPrice: Double,
	val quantityInStock: Int
)

Kotlin data class objects have some extra benefits, the compiler automatically generates utilities for comparing, printing and copying such as toString(), copy(), and equals().

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

• The primary constructor needs to have at least one parameter.
• All primary constructor parameters need to be marked as val or var.
• Data classes cannot be abstract, open, sealed or inner.

⚠️ The compiler only uses the properties defined inside the Primary constructor for the automatically generated functions. The properties declared inside the class body are excluded from the generated implementations.

To learn more about Data classes, check out the documentation.

copy() ​

The copy() function is provided by default to all the instances of data classes. This function is used to copy an object for changing some of its properties, but keeping the rest of the properties unchanged.

val newItem = item.copy(quantityInStock = item.quantityInStock - 1)