What Types Are

type declarations define reusable data shapes.

The most common form is an object type:

type User {
  id string
  email string
}

But a type can also be an alias for another type expression:

type UserId string
type Tags string[]
type Metadata map[string]

Object Types

Object types use braces and contain fields.

type Product {
  id string
  name string
  price float
  active bool
}

Each field is written as:

fieldName TypeName

There are no colons and no commas.

Optional Fields

Add ? after the field name to make a field optional.

type UserProfile {
  userId string
  displayName? string
  avatarUrl? string
}

Optional means the field may be absent in generated representations, depending on the target plugin.

Type Aliases

A type can name any valid field type.

type UserId string
type UserIds string[]
type UserMetadata map[string]

Aliases are useful when you want semantic names without repeating raw primitives everywhere.

type EmailAddress string

type User {
  id string
  email EmailAddress
}

Object Types Can Reference Other Types

type Address {
  line1 string
  line2? string
  city string
  country string
}

type Customer {
  id string
  billingAddress Address
  shippingAddress? Address
}

References must point to declared types or enums.

Inline Objects

Use an inline object when a nested shape is only useful in one place.

type CheckoutSession {
  id string
  payment {
    provider string
    amountCents int
    currency string
  }
}

Inline objects can contain fields, nested inline objects, and spreads.

Empty Objects

An object type can be empty, but it is rarely useful.

type EmptyObject {
}

Prefer adding fields when the contract has meaningful data.

Field Names Must Be Unique

Within an object or inline object, each field name must be unique.

Good:

type Product {
  id string
  sku string
}

Invalid:

type Product {
  id string
  id int
}

Naming

Type names should use PascalCase:

type UserProfile {
  displayName string
}

Field names should use camelCase:

type UserProfile {
  displayName string
  createdAt datetime
}

The analyzer reports diagnostics when names do not follow these conventions.