Intermediate LevelSoftware Engineering Principles
Why are Value Objects in Domain-Driven Design immutable and how do they enforce structural equality?
❓ Interview Prompt: Explain DDD Value Objects, immutability, structural equality vs identity equality, self-validation, and encapsulating domain concepts.
Value Objects represent domain concepts defined strictly by their attributes, lacking a unique identity ID (e.g. 'Money(10, 'USD')', 'DateRange'):
Core Properties:
1
Immutable: Once instantiated, Value Object properties CANNOT be mutated. State changes produce a new instance.
2
Structural Equality: Two Value Objects are equal if all their internal attribute values are identical ('valA.equals(valB)').
3
Self-Validating: Throw errors inside constructor if invariant rules are violated.
Code Implementation Example
typescript
class Money {
constructor(readonly amount: number, readonly currency: string) {
if (amount < 0) throw new Error('Amount cannot be negative');
Object.freeze(this); // Immutability guarantee!
}
equals(other: Money): boolean {
return this.amount === other.amount && this.currency === other.currency;
}
}💡Implementing an immutable, self-validating Money Value Object.
🎯 Interview Key Takeaway
Design Value Objects to be immutable and structurally equal to encapsulate domain concepts cleanly.
#Value Object#DDD#Immutability#Intermediate
Back to all Software Engineering Principles Questions→