go-types-conversion

Development

Naming convention for type-translation files and functions. Use when creating or editing files that convert between domain, API, and DB types.

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Type Translation Naming

Apply to new and touched code. Do not rename legacy symbols unsolicited.

File naming

Path contains	File name	Purpose
`httpdriver/`, `httphandler/`, `api/v3/handlers/`	`convert.go`	API ↔ domain
`adapter/`, `repo/`	`mapping.go`	DB ↔ domain

Split large files by entity: convert_plan.go, mapping_subscription.go.

mapper.go is forbidden. Rename it to convert.go or mapping.go (based on layer) when the file is touched.

Function naming

Shape: `From<Qualifier><Thing>` / `To<Qualifier><Thing>`

The qualifier is API or DB — no other qualifiers (Domain, Model, package-name infixes).

The suffix <Thing> is the non-domain type's unqualified name — the API type or DB type, not the domain type. This keeps it stable: a matched pair (FromAPI<Thing> / ToAPI<Thing>) always refers to the same non-domain type, regardless of direction.

FromAPI<Thing> — takes the API type <Thing> as input, returns the domain representation.
ToAPI<Thing> — takes the domain type as input, returns the API type <Thing>.
Same for FromDB<Thing> / ToDB<Thing>.

Examples

// API ↔ domain
FromAPIPlan(a api.Plan) (plan.Plan, error)
ToAPIPlan(p plan.Plan) api.Plan

// Suffix is the API type name, even when domain type differs
FromAPIPlanCreate(a api.PlanCreate) (plan.CreateInput, error)
ToAPIPlanCreate(p plan.CreateInput) api.PlanCreate

FromAPIProRatingConfig(a api.ProRatingConfig) (productcatalog.ProRatingConfig, error)
ToAPIProRatingConfig(p productcatalog.ProRatingConfig) *api.ProRatingConfig

// DB ↔ domain — suffix is the DB type name
FromDBSubscription(row *db.Subscription) (subscription.Subscription, error)
ToDBSubscription(s subscription.Subscription) *db.Subscription

FromDBChargeFlatFee(row *entdb.ChargeFlatFee) (flatfee.Charge, error)
ToDBChargeFlatFee(c flatfee.Charge) *entdb.ChargeFlatFee

Additional rules

Exported functions always include the type suffix (FromAPIPlanCreate, not bare FromAPI).
Unexported helpers in a single-type file may drop the suffix (fromDB, toAPI).
Fallible (parse/validate) → (T, error). Infallible (projection) → T. Typically FromAPI… / FromDB… is fallible; the reverse is not.
Batch helpers use the plural: FromAPIPlans, ToDBSubscriptions. Same suffix rule — the plural of the non-domain type name.

Forbidden patterns

Map…, Convert…To…, primary As…
<Source>To<Target> shape (e.g. APIToPlan)
Bare FromAPI / ToDB without a type suffix
goverter or other codegen type mappers

Decision tree

Naming a function

Pick the qualifier: API/HTTP/wire on one side → API. DB/persistence on one side → DB.
Pick the suffix: the non-domain type's unqualified name (Plan, PlanCreate, ChargeFlatFee).
Pick the return style: fallible → (T, error), infallible → T.
Exported? Must include the type suffix. Unexported single-type helper may drop it.

Interacting with the user

File is mapper.go? Flag it — should be convert.go or mapping.go based on layer. Offer to rename as part of the edit. Don't rename silently.
Adding new functions to a legacy file? Use the new convention for new functions. Don't rename old ones unless asked.
Task is "clean up this file"? Rename, update call sites, Grep for the old name to catch misses, keep the rename in its own commit.
// Code generated header? Off-limits regardless.

Suggestion phrasing

Lead with the specific rename and the reason. Keep it short.

MapChargeFlatFeeFromDB — use FromDBChargeFlatFee. Want me to rename and update callers?

Direction looks inverted — FromAPI… returns a domain type, so this should be ToAPIPlan. Drop the error return if it can't actually fail.

This file is mapper.go — should be convert.go since it lives in httphandler/. Want me to rename it?