effect-io-ai

Package: effect
Module: Newtype

Newtype.Newtype

A tagged interface that wraps a carrier type under a unique key, preventing accidental interchange of structurally identical values.

When to use

Use to define a newtype as an interface extending Newtype<"MyKey", CarrierType> when structurally identical carrier types should remain distinct in TypeScript.

Details

The tag is compile-time only, so no runtime wrapper is allocated. Use makeIso to create a two-way conversion, or value to unwrap.

Example (Defining a newtype)

import { Newtype } from "effect"

interface UserId extends Newtype.Newtype<"UserId", number> {}
interface OrderId extends Newtype.Newtype<"OrderId", number> {}

// UserId and OrderId are not assignable to each other
// even though both wrap `number`.

See

• makeIso — create an iso to wrap and unwrap
• value — unwrap a newtype value

Signature

export interface Newtype<in out Key extends string, out Carrier> {
  readonly [TypeId]: {
    readonly key: Key
    readonly carrier: Carrier
  }
}

Source

Since v4.0.0