ReadonlyStruct overview

This module targets readonly objects in the sense of product types. For readonly objects in the sense of maps see the Record module.

Added in v0.14.0

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Table of contents

• 3 Functions
  • get
  • merge
  • omit
  • omitFrom
  • pick
  • pickFrom
  • renameKey
  • withDefaults

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3 Functions

get

Get the value for a key in a struct.

Signature

export declare const get: <K extends string>(k: K) => <A>(x: Readonly<Record<K, A>>) => A

get :: k extends string => k -> Readonly (Record k a) -> a

Example

import { get } from 'fp-ts-std/Struct'

type Person = { name: string; age: number }
const person: Person = { name: 'Albert', age: 76 }

const getName = get('name')

assert.strictEqual(getName(person), 'Albert')

Added in v0.17.0

merge

Merge two readonly structs together. For merging many identical structs, instead consider defining a semigroup.

Signature

export declare const merge: <A, B>(x: A) => <C extends B>(y: C) => A & C

merge :: c extends b => a -> c -> a & c

Example

import { merge } from 'fp-ts-std/ReadonlyStruct'

assert.deepStrictEqual(merge({ a: 1, b: 2 })({ b: 'two', c: true }), { a: 1, b: 'two', c: true })

Added in v0.14.0

omit

Omit a set of keys from a readonly struct. The value-level equivalent of the Omit type.

Signature

export declare const omit: <K extends string>(
  ks: readonly K[]
) => <V, A extends Readonly<Record<K, V>>>(x: A) => Pick<A, Exclude<keyof A, K>>

omit :: k extends string, a extends (Readonly (Record k v)) => Array k -> a -> Pick a (Exclude (keyof a) k)

Example

import { omit } from 'fp-ts-std/ReadonlyStruct'

const sansB = omit(['b'])

assert.deepStrictEqual(sansB({ a: 1, b: 'two', c: [true] }), { a: 1, c: [true] })

Added in v0.14.0

omitFrom

Like omit, but allows you to specify the input struct upfront.

Signature

export declare const omitFrom: <A>() => <K extends keyof A & string>(
  ks: readonly K[]
) => (x: A) => Pick<A, Exclude<keyof A, K>>

omitFrom :: k extends ((keyof a) & string) => () -> Array k -> a -> Pick a (Exclude (keyof a) k)

Example

import { omitFrom } from 'fp-ts-std/ReadonlyStruct'

type MyType = { a: number; b: string; c: ReadonlyArray<boolean> }
const sansB = omitFrom<MyType>()(['b'])

assert.deepStrictEqual(sansB({ a: 1, b: 'two', c: [true] }), { a: 1, c: [true] })

Added in v0.15.0

pick

Pick a set of keys from a readonly struct. The value-level equivalent of the Pick type.

Signature

export declare const pick: <A extends object, K extends keyof A>(ks: readonly K[]) => (x: A) => Pick<A, K>

pick :: a extends object, k extends (keyof a) => Array k -> a -> Pick a k

Example

import { pick } from 'fp-ts-std/ReadonlyStruct'
import { pipe } from 'fp-ts/function'

const picked = pipe({ a: 1, b: 'two', c: [true] }, pick(['a', 'c']))

assert.deepStrictEqual(picked, { a: 1, c: [true] })

Added in v0.14.0

pickFrom

Like pick, but allows you to specify the input struct upfront.

Signature

export declare const pickFrom: <A extends object>() => <K extends keyof A>(ks: readonly K[]) => (x: A) => Pick<A, K>

pickFrom :: a extends object, k extends (keyof a) => () -> Array k -> a -> Pick a k

Example

import { pickFrom } from 'fp-ts-std/ReadonlyStruct'

type MyType = { a: number; b: string; c: ReadonlyArray<boolean> }
const picked = pickFrom<MyType>()(['a', 'c'])

assert.deepStrictEqual(picked({ a: 1, b: 'two', c: [true] }), { a: 1, c: [true] })

Added in v0.14.0

renameKey

Rename a key in a struct, preserving the value. If the new key already exists, the old key will be overwritten. Optionality is preserved.

Signature

export declare const renameKey: <I extends string>(
  oldK: I
) => <J extends string>(
  newK: J
) => <A extends MaybePartial<Readonly<Record<I, unknown>>>>(
  x: A
) => Readonly<{ [K in keyof A as K extends I ? J : K]: A[K] }>

renameKey :: i extends string, j extends string, a extends (MaybePartial (Readonly (Record i unknown))) => i -> j -> a -> Readonly { [k in (keyof a) as k extends i ? j : k]: a[k] }

Example

import { renameKey } from 'fp-ts-std/Struct'

type Foo = { a: string; b: number }
type Bar = { a: string; c: number }

const fooBar: (x: Foo) => Bar = renameKey('b')('c')

Added in v0.15.0

withDefaults

Provide default values for an object with optional properties.

Signature

export declare const withDefaults: <
  T extends Readonly<Record<string, unknown>>,
  PT extends Exact<{ [K in OptionalKeys<T>]-?: Exclude<T[K], undefined> }, PT>
>(
  defaults: PT
) => (t: T) => Readonly<PT & T>

Example

import { withDefaults } from 'fp-ts-std/ReadonlyStruct'
import { pipe } from 'fp-ts/function'

const aOptB: { a: number; b?: string } = { a: 1 }

assert.deepStrictEqual(pipe(aOptB, withDefaults({ b: 'foo' })), { a: 1, b: 'foo' })

Added in v0.15.0