Come usare
- Copia il comando e controlla il pacchetto prima di installarlo nel tuo ambiente agente.
- Controlla strumenti, credenziali e ambienti richiesti nel documento originale.
- Descrivi input e risultato desiderato; confronta l’output con le fonti.
npx skills add https://github.com/yonatankarp/software-design-skills --skill gof-prototypePrima di iniziare
- L’installazione non include abbonamenti, quote API o accesso ai file.
- Stelle e installazioni indicano attività, non un test indipendente di qualità o sicurezza.
Contenuto dal repository con titoli, esempi, codice, tabelle, link e immagini preservati.
One-line summary
Create new objects by copying an existing instance (the prototype) rather than by calling a constructor — useful when construction is expensive, when you only want to vary a few fields, or when you have a registry of canned shapes.
When to use this skill
- Object construction is expensive or has side effects that you don't want repeated.
- You have a "template" instance and want variations of it with a few fields changed.
- You need a registry of canned instances that consumers can clone and customize.
- The canonical Kotlin manifestation:
data class.copy(field = newValue)is exactly this pattern.
When NOT to use this skill
- Construction is cheap and stateless — just call the constructor.
- The "copy" must be a deep clone of a complex object graph — Prototype's contract is usually a shallow copy; deep cloning is its own problem.
- You're trying to dodge a hard construction problem by "copying" something that doesn't really exist yet — that's a smell.
Core content
Two flavors:
Simple Prototype. The object has a clone() (or copy()) method that returns a new instance with the same field values. Callers obtain a base instance, copy it, and mutate the copy. In Kotlin, every data class provides copy() for free, optionally with named-argument overrides.
val baseRequest = HttpRequest(method = GET, url = "/users", headers = standardHeaders)
val authedRequest = baseRequest.copy(headers = standardHeaders + auth)Prototype Registry. A central registry holds named prototype instances. Consumers ask the registry for a prototype by name ("weekday-shift", "weekend-shift") and get a clone they can customize. Useful when prototypes are configuration data rather than code.
The pattern's value is making intent obvious: "this new instance is like that existing one, with these differences" reads better than reconstructing every field.
Decision heuristics
- In Kotlin,
data class.copy()is the default Prototype. Reach for an explicit registry only when prototypes are named, configured, or numerous. - For non-
data classtypes, decide deliberately whethercopy()should be a deep or shallow copy and document it. - Beware of nested mutable state —
copy()of adata classcopies the references, not the referenced objects. Mutating a shared nested list breaks both the original and the copy.
Anti-patterns
clone()methods that are almost but not exactly a copy — accidentally produce subtly different instances. Either copy exactly or rename the method.- Mutable prototypes shared across consumers without copying — the registry's instances drift over time.
- Implementing Prototype as a workaround for a missing constructor — fix the constructor instead.
See also
gof-factory— sometimes the right answer instead of Prototype, especially when each "variation" is really a different concrete type.gof-builder— when the variations are structural (different steps), not field-level overrides.gof-kotlin-idioms—data class.copy()is Prototype-as-language-feature.
References
- Design Patterns (GoF, 1994), Ch. 3 — Prototype. (Not in HFDP 2nd ed.)
- Kotlin Design Patterns and Best Practices (Alexey Soshin), Ch. 2 — Prototype, framed around Kotlin's
copy().
