70. Value classes in Kotlin

🔍 Value Classes in Kotlin: Deep Dive into Lightweight Wrappers

Welcome, Kotlin developers! Today we'll explore one of the most powerful and efficient features in Kotlin - Value Classes. These lightweight wrappers provide an elegant solution for creating type-safe abstractions without additional runtime overhead.

📘 Understanding Value Classes

Value classes, introduced in Kotlin 1.5, allow developers to create wrapper types that are fully inlined by the compiler, eliminating unnecessary object allocation and improving performance.

@JvmInline
value class Username(val value: String)

@JvmInline
value class UserId(val value: Long)

🚀 Key Characteristics

  • Zero runtime allocation
  • Type-safe wrapper for primitive types
  • Compiler optimization
  • Improved code readability
  • Prevents incorrect type usage

💡 Practical Implementation Scenarios

Value classes shine in scenarios requiring type distinction without performance overhead:

@JvmInline
value class Email(val address: String) {
    init {
        require(address.contains("@")) { "Invalid email format" }
    }
}

@JvmInline
value class Money(val amount: Double) {
    operator fun plus(other: Money) = Money(amount + other.amount)
}

🔬 Limitations and Constraints

  • Must have single constructor parameter
  • Cannot inherit from other classes
  • Limited to primitive types and String
  • No additional properties allowed (except computed properties)

🏗️ Performance Comparison

Traditional wrapper vs Value Class:

// Traditional Wrapper (Overhead)
class TraditionalEmail(val address: String)

// Value Class (Zero Overhead)
@JvmInline
value class OptimizedEmail(val address: String)

🎯 Practical Exercises

  1. Create a Phone Number value class with validation
  2. Implement a Temperature value class with conversion methods
  3. Design an Age value class preventing negative values
  4. Build a Weight value class supporting different units
  5. Develop a Transaction Amount value class with arithmetic operations

⚠️ Common Pitfalls

Warning: Value classes cannot be used with generics or as type parameters.

📋 Best Practices

  • Use for type safety and semantic meaning
  • Prefer immutable implementations
  • Add validation in init block
  • Consider performance implications

🔮 Future of Value Classes

Kotlin continues to evolve, with potential future enhancements to make value classes even more powerful and flexible.

#Kotlin #ValueClasses #Performance #TypeSafety

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