Schema.Opaque — API

Schema.Opaquefunctioneffect/Schema.ts:6278

Opaque<Self, S, Brand>

Wraps a struct schema so that its decoded Type becomes a nominally distinct type Self. Useful for creating opaque types that are structurally identical to a base struct but type-incompatible with it.

Example (Defining opaque structs)

import { Schema } from "effect"

class Person extends Schema.Opaque<Person>()(
  Schema.Struct({
    name: Schema.String
  })
) {}

// Decoded value is Person, not { name: string }
const person = Schema.decodeUnknownSync(Person)({ name: "Alice" })
// person: Person

constructors

Source effect/Schema.ts:627853 lines

export interface Opaque<Self, S extends Top, Brand> extends
  BottomLazy<
    S["ast"],
    S["Rebuild"],
    S["~type.parameters"],
    S["~type.mutability"],
    S["~type.optionality"],
    S["~type.constructor.default"],
    S["~encoded.mutability"],
    S["~encoded.optionality"]
  >
{
  readonly "Type": Self
  readonly "Encoded": S["Encoded"]
  readonly "DecodingServices": S["DecodingServices"]
  readonly "EncodingServices": S["EncodingServices"]
  readonly "~type.make.in": S["~type.make.in"]
  readonly "~type.make": S["~type.make"]
  readonly "Iso": S["Iso"]
  new(_: never): S["Type"] & Brand
}

/**
 * Wraps a struct schema so that its decoded `Type` becomes a nominally distinct type `Self`.
 * Useful for creating opaque types that are structurally identical to a base struct
 * but type-incompatible with it.
 *
 * **Example** (Defining opaque structs)
 *
 * ```ts
 * import { Schema } from "effect"
 *
 * class Person extends Schema.Opaque<Person>()(
 *   Schema.Struct({
 *     name: Schema.String
 *   })
 * ) {}
 *
 * // Decoded value is Person, not { name: string }
 * const person = Schema.decodeUnknownSync(Person)({ name: "Alice" })
 * // person: Person
 * ```
 *
 * @category constructors
 * @since 4.0.0
 */
export function Opaque<Self, Brand = {}>() {
  return <S extends Top>(schema: S): Opaque<Self, S, Brand> & Omit<S, keyof Top> => {
    // oxlint-disable-next-line @typescript-eslint/no-extraneous-class
    class Opaque {}
    return Object.setPrototypeOf(Opaque, schema)
  }
}