Is it possible to apply the keyword abstract to a data class in programming languages that support both concepts?

In programming languages that support both concepts — abstract classes and data classes (for example, Kotlin), the keyword abstract can be applied to data classes, but with restrictions.

However, in Kotlin, for example, a data class cannot be abstract because:

• A data class is intended for storing data with automatically generated methods (equals, hashCode, toString, copy).
• An abstract class cannot be instantiated directly, and a data class requires implementation of all properties for method generation.

If you need to create an abstract class with similar properties, it's better to use a regular abstract class without data.

Example (Kotlin):

// Compilation error
abstract data class User(val name: String)

// Correct approach
abstract class User(val name: String)

Thus, generally, you cannot apply abstract to a data class.