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data

Brand overview

This module provides types and utility functions to create and work with branded types, which are TypeScript types with an added type tag to prevent accidental usage of a value in the wrong context.

The refined and nominal functions are both used to create branded types in TypeScript. The main difference between them is that refined allows for validation of the data, while nominal does not.

The nominal function is used to create a new branded type that has the same underlying type as the input, but with a different name. This is useful when you want to distinguish between two values of the same type that have different meanings. The nominal function does not perform any validation of the input data.

On the other hand, the refined function is used to create a new branded type that has the same underlying type as the input, but with a different name, and it also allows for validation of the input data. The refined function takes a predicate that is used to validate the input data. If the input data fails the validation, a BrandErrors is returned, which provides information about the specific validation failure.

Added in v1.0.0

Table of contents

alias

Branded (type alias)

Signature

export type Branded<A, K extends string | symbol> = A & Brand<K>

Added in v1.0.0

combining

all

Combines two or more brands together to form a single branded type. This API is useful when you want to validate that the input data passes multiple brand validators.

Signature

export declare const all: <Brands extends readonly [Brand.Constructor<any>, ...Brand.Constructor<any>[]]>(
  ...brands: Brand.EnsureCommonBase<Brands>
) => Brand.Constructor<
  Types.UnionToIntersection<
    { [B in keyof Brands]: Brand.FromConstructor<Brands[B]> }[number]
  > extends infer X extends Brand<any>
    ? X
    : Brand<any>
>

Example

import * as Brand from '@effect/data/Brand'

type Int = number & Brand.Brand<'Int'>
const Int = Brand.refined<Int>(
  (n) => Number.isInteger(n),
  (n) => Brand.error(`Expected ${n} to be an integer`)
)
type Positive = number & Brand.Brand<'Positive'>
const Positive = Brand.refined<Positive>(
  (n) => n > 0,
  (n) => Brand.error(`Expected ${n} to be positive`)
)

const PositiveInt = Brand.all(Int, Positive)

assert.strictEqual(PositiveInt(1), 1)
assert.throws(() => PositiveInt(1.1))

Added in v1.0.0

constructors

error

Returns a BrandErrors that contains a single RefinementError.

Signature

export declare const error: (message: string, meta?: unknown) => Brand.BrandErrors

Added in v1.0.0

errors

Takes a variable number of BrandErrors and returns a single BrandErrors that contains all refinement errors.

Signature

export declare const errors: (...errors: Array<Brand.BrandErrors>) => Brand.BrandErrors

Added in v1.0.0

nominal

This function returns a Brand.Constructor that does not apply any runtime checks, it just returns the provided value. It can be used to create nominal types that allow distinguishing between two values of the same type but with different meanings.

If you also want to perform some validation, see {@link refined}.

Signature

export declare const nominal: <A extends Brand<any>>() => Brand.Constructor<A>

Example

import * as Brand from '@effect/data/Brand'

type UserId = number & Brand.Brand<'UserId'>

const UserId = Brand.nominal<UserId>()

assert.strictEqual(UserId(1), 1)

Added in v1.0.0

refined

Returns a Brand.Constructor that can construct a branded type from an unbranded value using the provided refinement predicate as validation of the input data.

If you don’t want to perform any validation but only distinguish between two values of the same type but with different meanings, see {@link nominal}.

Signature

export declare const refined: <A extends Brand<any>>(
  refinement: Predicate<Brand.Unbranded<A>>,
  onFailure: (a: Brand.Unbranded<A>) => Brand.BrandErrors
) => Brand.Constructor<A>

Example

import * as Brand from '@effect/data/Brand'

type Int = number & Brand.Brand<'Int'>

const Int = Brand.refined<Int>(
  (n) => Number.isInteger(n),
  (n) => Brand.error(`Expected ${n} to be an integer`)
)

assert.strictEqual(Int(1), 1)
assert.throws(() => Int(1.1))

Added in v1.0.0

models

Brand (interface)

A generic interface that defines a branded type.

Signature

export interface Brand<in out K extends string | symbol> {
  readonly [BrandTypeId]: {
    readonly [k in K]: K
  }
}

Added in v1.0.0

symbols

BrandTypeId

Signature

export declare const BrandTypeId: typeof BrandTypeId

Added in v1.0.0

BrandTypeId (type alias)

Signature

export type BrandTypeId = typeof BrandTypeId

Added in v1.0.0

RefinedConstructorsTypeId

Signature

export declare const RefinedConstructorsTypeId: typeof RefinedConstructorsTypeId

Added in v1.0.0

RefinedConstructorsTypeId (type alias)

Signature

export type RefinedConstructorsTypeId = typeof RefinedConstructorsTypeId

Added in v1.0.0

utils

Brand (namespace)

Added in v1.0.0

BrandErrors (interface)

Represents a list of refinement errors.

Signature

export interface BrandErrors extends ReadonlyArray<RefinementError> {}

Added in v1.0.0

Constructor (interface)

Signature

export interface Constructor<in out A extends Brand<any>> {
  readonly [RefinedConstructorsTypeId]: RefinedConstructorsTypeId
  /**
   * Constructs a branded type from a value of type `A`, throwing an error if
   * the provided `A` is not valid.
   */
  (args: Brand.Unbranded<A>): A
  /**
   * Constructs a branded type from a value of type `A`, returning `Some<A>`
   * if the provided `A` is valid, `None` otherwise.
   */
  option: (args: Brand.Unbranded<A>) => Option.Option<A>
  /**
   * Constructs a branded type from a value of type `A`, returning `Right<A>`
   * if the provided `A` is valid, `Left<BrandError>` otherwise.
   */
  either: (args: Brand.Unbranded<A>) => Either.Either<Brand.BrandErrors, A>
  /**
   * Attempts to refine the provided value of type `A`, returning `true` if
   * the provided `A` is valid, `false` otherwise.
   */
  is: Refinement<Brand.Unbranded<A>, Brand.Unbranded<A> & A>
}

Added in v1.0.0

RefinementError (interface)

Represents an error that occurs when the provided value of the branded type does not pass the refinement predicate.

Signature

export interface RefinementError {
  readonly meta: unknown
  readonly message: string
}

Added in v1.0.0

Brands (type alias)

A utility type to extract the brands from a branded type.

Signature

export type Brands<P> = P extends Brand<any>
  ? Types.UnionToIntersection<
      {
        [k in keyof P[BrandTypeId]]: k extends string | symbol ? Brand<k> : never
      }[keyof P[BrandTypeId]]
    >
  : never

Added in v1.0.0

EnsureCommonBase (type alias)

A utility type that checks that all brands have the same base type.

Signature

export type EnsureCommonBase<Brands extends readonly [Brand.Constructor<any>, ...Array<Brand.Constructor<any>>]> = {
  [B in keyof Brands]: Brand.Unbranded<Brand.FromConstructor<Brands[0]>> extends Brand.Unbranded<
    Brand.FromConstructor<Brands[B]>
  >
    ? Brand.Unbranded<Brand.FromConstructor<Brands[B]>> extends Brand.Unbranded<Brand.FromConstructor<Brands[0]>>
      ? Brands[B]
      : Brands[B]
    : 'ERROR: All brands should have the same base type'
}

Added in v1.0.0

FromConstructor (type alias)

A utility type to extract a branded type from a Brand.Constructor.

Signature

export type FromConstructor<A> = A extends Brand.Constructor<infer B> ? B : never

Added in v1.0.0

Unbranded (type alias)

A utility type to extract the value type from a brand.

Signature

export type Unbranded<P> = P extends infer Q & Brands<P> ? Q : P

Added in v1.0.0