Why aren't models plain structs?

Primary source: ADR 002 — Backing-store-backed models.

The decision

Models aren't plain structs. Every model embeds core.BaseModel and stores its data in a Kiota BackingStore — a key/value store with change tracking — rather than in struct fields. Accessors are generated from the helpers in internal/store (DefaultBackedModelAccessorFunc / DefaultBackedModelMutatorFunc), so every property is a GetX() (T, error) / setX(T) error pair around the store.

This replaced plain struct fields during the v2 rework (PR #474).

Why

• Absent ≠ zero. ServiceNow omits fields freely (and sysparm_fields makes it routine). A struct field can't distinguish "the instance sent an empty string" from "the instance didn't send this field"; a store lookup can, which is why getters return pointers and errors.
• Dirty tracking. The store records which properties changed, so a Put/Patch body serializes only the fields the caller actually set — not a full struct with zero values that would overwrite server data.
• Kiota parity. The SDK deliberately matches the conventions of Kiota-generated SDKs (msgraph-sdk-go and friends). Backed models are how those SDKs behave; deviating would make this the one Kiota-style SDK whose models act differently.

What to do in new code

• Embed core.BaseModel; never add plain data fields to a model.
• Build each accessor pair on internal/store helpers, and each Serialize/GetFieldDeserializers on the internal/serialization generators — no hand-rolled property plumbing.
• Generic code should constrain models with model.ServiceNowItem (store.BackedModel + serialization.Parsable + GetSysID()).

The user-facing consequence of this design is the pointer-and-error getter pattern explained in Core Concepts.