Spreads and References

References

A reference points to a named VDL symbol.

References appear in several places:

• field types
• spreads
• constant values
• annotation arguments

Type References

Fields can reference declared types.

type UserId string

type User {
  id UserId
}

Fields can also reference enums.

enum Status {
  Active
  Disabled
}

type User {
  status Status
}

Constant References

Constants can reference other constants by name.

const defaultLimit = 100
const pageSize = defaultLimit

Enum Member References

Use EnumName.MemberName to reference an enum member in literal values.

enum Status {
  Active = "active"
  Disabled = "disabled"
}

const defaultStatus = Status.Active

Type Spreads

Type spreads copy fields from another object type.

type AuditFields {
  createdAt datetime
  updatedAt datetime
}

type Article {
  ...AuditFields
  id string
  title string
}

After analysis, plugins see Article as if it had all fields directly.

Only object types can be spread into object types.

Invalid:

type UserId string

type User {
  ...UserId
  name string
}

Inline Object Spreads

Inline objects can also spread object types.

type Money {
  amount int
  currency string
}

type Order {
  id string
  payment {
    ...Money
    provider string
  }
}

Field Conflicts

Spreads cannot introduce a field that already exists in the same object.

Invalid:

type BaseUser {
  id string
}

type User {
  ...BaseUser
  id string
}

Rename one field or avoid the spread.

Enum Spreads

Enum spreads copy members from another enum.

enum StandardRole {
  Viewer = "viewer"
  Editor = "editor"
}

enum ProjectRole {
  ...StandardRole
  Owner = "owner"
}

Enum spreads must reference enums, not enum members.

Invalid:

enum Role {
  Viewer = "viewer"
}

enum ProjectRole {
  ...Role.Viewer
  Owner = "owner"
}

Object Literal Spreads

Object literals can spread constant objects.

const baseConfig = {
  retries 3
  timeoutMs 5000
}

const productionConfig = {
  ...baseConfig
  timeoutMs 10000
}

Only object constants can be used this way.

Spread Cycles

Spreads cannot form cycles.

Invalid:

type A {
  ...B
  a string
}

type B {
  ...A
  b string
}

Keep spread hierarchies simple and acyclic.

Name Forms

VDL supports two reference forms:

Spreads must use Name, not Name.Member.