Named Brands

What Named Brands Do

By default, brand types are anonymous — String() returns just the value. Adding a Name() method enables:

• Debug-visible IDs: String() returns "User:abc123" instead of just "abc123"
• Brand-aware validation: ValidateID errors include the brand name
• Runtime introspection: BrandName[T]() for logging and error messages

Defining a Named Brand

type UserBrand struct{}

func (UserBrand) Name() string { return "User" }

That’s it. The Name() method is the entire BrandNamer interface.

String Output

userID := id.NewID[UserBrand]("abc123")
fmt.Println(userID)               // User:abc123
fmt.Printf("%#v\n", userID)       // id.User(abc123)

// Unnamed brand (no Name() method)
orderID := id.NewID[OrderBrand]("order-456")
fmt.Println(orderID)              // order-456 (value only)

GoString() and %#v output is a display format, not valid Go syntax.

Validation

var empty ID[UserBrand, string]
err := id.ValidateID(empty)
fmt.Println(err) // id: invalid: User: empty

// With a custom value validator
err = id.ValidateIDWithValue(userID, func(v string) error {
    if v == "" { return errors.New("required") }
    return nil
})

// Panic variant for init-time checks
id.MustValidateID(userID)

Introspection

fmt.Println(id.BrandName[UserBrand]()) // User

For unnamed brands, BrandName falls back to fmt.Sprintf("%T", brand) — which includes the package path (e.g., "main.OrderBrand").

String() vs Get()

Method	Returns	Use Case
String()	"User:abc123"	Display, logging
Get()	"abc123"	Programmatic value extraction

Serialization never uses String(). JSON, SQL, Text, Binary, and Gob all use the raw value internally. Adding Name() does not affect serialized output.

Adding Name() to Existing Brands

If you add Name() to a brand that didn’t have it before, String() changes behavior. Any code parsing String() output will break — but code using Get() is unaffected.

Rule: Use Get() for any programmatic value extraction. Use String() only for display and logging.