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Sum type

Sum type (also known as tagged union) is a type that can be one of multiple possible variants. ogen uses sum types to represent oneOf and some anyOf schemas.

oneOf schema
Sum:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'
Generated sum type
// Sum represents sum type.
type Sum struct {
    Type SumType // switch on this field
    Cat  Cat
    Dog  Dog
}

// SumType is oneOf type of Sum.
type SumType string

// Possible values for SumType.
const (
    CatSum SumType = "Cat"
    DogSum SumType = "Dog"
)

Discriminator inference​

To distinguish different cases, decoder need some pattern called discriminator.

Explicit discriminator​

Generator may distinguish variants by special type field.

oneOf schema with explicit discriminator mapping
Sum:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'
  discriminator:
    propertyName: petType
    mapping:
      cat: '#/components/schemas/Cat'
      dog: '#/components/schemas/Dog'

Type discriminator​

Type discriminator is discriminator based on JSON type.

oneOf schema with type discriminator
ID:
  oneOf:
  - type: string
  - type: integer

Unique fields discriminator​

Unique fields discriminator is discriminator based on unique schema fields. In that case, Decoder select variant by field that available only in one of all variants.

For example, given that schema:

oneOf schema with unique fields discriminator
Sum:
  oneOf:
  - type: object
    required:
    - common-1
    - unique-1
    properties:
      common-1:
        type: string
      unique-1:
        type: string
  - type: object
    required:
    - common-1
    - unique-2
    properties:
      common-1:
        type: string
      unique-2:
        type: string

a payload like this:

{"common-1": "foo", "unique-1": "bar"}

will indicate that the first variant be used.