Delegated properties (`by`): what problem do they solve?

Deep dive

Expanding on the short answer — what usually matters in practice:

• Context (tags): kotlin, delegation, properties, observable
• JVM: memory (heap/stack), GC, and what drives latency.
• Contracts: equals/hashCode/toString, mutability and consequences.
• Performance: boxing, allocations, collections, inlining.
• Explain the "why", not just the "what" (intuition + consequences).
• Trade-offs: what you gain/lose (time, memory, complexity, risk).
• Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

Here’s an additional example (building on the short answer):

var name: String by Delegates.observable("<init>") { _, old, new ->
  println("$old -> $new")
}

name = "Ala"

Common pitfalls

• Too generic: no concrete trade-offs or examples.
• Mixing average-case and worst-case (e.g., complexity).
• Ignoring constraints: memory, concurrency, network/disk costs.

Interview follow-ups

• When would you choose an alternative and why?
• What production issues show up and how do you diagnose them?
• How would you test edge cases?