feat: Add a function that combines multiple results and returns an object

Author: Karibash

.changeset/thin-wolves-notice.md

@@ -0,0 +1,5 @@
+---
+'neverthrow': minor
+---
+
+Add a function that combines multiple results and returns an object.

README.md

@@ -41,6 +41,7 @@ For asynchronous tasks, `neverthrow` offers a `ResultAsync` class which wraps a
     - [`Result.fromThrowable` (static class method)](#resultfromthrowable-static-class-method)
     - [`Result.combine` (static class method)](#resultcombine-static-class-method)
     - [`Result.combineWithAllErrors` (static class method)](#resultcombinewithallerrors-static-class-method)
+    - [`Result.struct` (static class method)](#resultstruct-static-class-method)
     - [`Result.safeUnwrap()`](#resultsafeunwrap)
   + [Asynchronous API (`ResultAsync`)](#asynchronous-api-resultasync)
     - [`okAsync`](#okasync)
@@ -58,6 +59,7 @@ For asynchronous tasks, `neverthrow` offers a `ResultAsync` class which wraps a
     - [`ResultAsync.andThrough` (method)](#resultasyncandthrough-method)
     - [`ResultAsync.combine` (static class method)](#resultasynccombine-static-class-method)
     - [`ResultAsync.combineWithAllErrors` (static class method)](#resultasynccombinewithallerrors-static-class-method)
+    - [`ResultAsync.struct` (static class method)](#resultasyncstruct-static-class-method)
     - [`ResultAsync.safeUnwrap()`](#resultasyncsafeunwrap)
   + [Utilities](#utilities)
     - [`fromThrowable`](#fromthrowable)
@@ -800,6 +802,59 @@ const result = Result.combineWithAllErrors(resultList)
 
 [⬆️  Back to top](#toc)
 
+---
+
+#### `Result.struct` (static class method)
+
+> Although Result is not an actual JS class, the way that `struct` has been implemented requires that you call `struct` as though it were a static method on `Result`. See examples below.
+
+Combine objects of `Result`s.
+
+**`struct` works on both heterogeneous and homogeneous objects**. This means that you can have objects that contain different kinds of `Result`s and still be able to combine them. Note that you cannot combine objects that contain both `Result`s **and** `ResultAsync`s.
+
+The `struct` function takes an object of results and returns a single result. If all the results in the object are `Ok`, then the return value will be a `Ok` containing an object of all the individual `Ok` values.
+
+If multiple results in the object are `Err` then the `struct` function returns an `Err` containing an array of all the error values.
+
+Example:
+```typescript
+const resultObject: {
+  a: Result<number, never>
+  b: Result<number, never>
+} = {
+  a: ok(1),
+  b: ok(2),
+}
+
+const combinedList: Result<{
+  a: number
+  b: number
+}, never> = Result.struct(resultObject)
+```
+
+Example of error:
+```typescript
+const resultObject: {
+  a: Result<number, unknown>
+  b: Result<never, number>
+  c: Result<never, string>
+} = {
+  a: ok(1),
+  b: err(2),
+  c: err('3'),
+}
+
+const combinedList: Result<{
+  a: number
+  b: unknown
+  c: unknown
+}, (number | number)[]> = Result.struct(resultObject)
+```
+
+[⬆️  Back to top](#toc)
+
+---
+
 #### `Result.safeUnwrap()`
 
 **Deprecated**. You don't need to use this method anymore.
@@ -1410,6 +1465,57 @@ const result = ResultAsync.combineWithAllErrors(resultList)
 // result is Err(['boooom!', 'ahhhhh!'])
 ```
 
+---
+
+#### `ResultAsync.struct` (static class method)
+
+Combine objects of `ResultAsyncs`s.
+
+**`struct` works on both heterogeneous and homogeneous objects**. This means that you can have objects that contain different kinds of `Result`s and still be able to combine them. Note that unlike `Result.struct`, you can combine objects containing both `Result`s and `ResultAsync`s.
+
+The `struct` function takes an object of results and returns a single result. If all the results in the object are `Ok`, then the return value will be a `Ok` containing an object of all the individual `Ok` values.
+
+If multiple results in the object are `Err` then the `struct` function returns an `Err` containing an array of all the error values.
+
+Example:
+```typescript
+const resultObject: {
+  a: ResultAsync<number, never>
+  b: ResultAsync<number, never>
+} = {
+  a: okAsync(1),
+  b: okAsync(2),
+}
+
+const combinedList: ResultAsync<{
+  a: number
+  b: number
+}, never> = ResultAsync.struct(resultObject)
+```
+
+Example of error:
+```typescript
+const resultObject: {
+  a: ResultAsync<number, unknown>
+  b: ResultAsync<never, number>
+  c: ResultAsync<never, string>
+} = {
+  a: okAsync(1),
+  b: errAsync(2),
+  c: errAsync('3'),
+}
+
+const combinedList: ResultAsync<{
+  a: number
+  b: unknown
+  c: unknown
+}, (number | number)[]> = ResultAsync.struct(resultObject)
+```
+
+[⬆️  Back to top](#toc)
+
+---
+
 #### `ResultAsync.safeUnwrap()`
 
 **Deprecated**. You don't need to use this method anymore.

src/_internals/utils.ts

@@ -21,12 +21,17 @@ export type ExtractErrAsyncTypes<T extends readonly ResultAsync<unknown, unknown
   [idx in keyof T]: T[idx] extends ResultAsync<unknown, infer E> ? E : never
 }
 
+export type MaybeResultAsync<T, E> = ResultAsync<T, E> | Result<T, E>
+
 export type InferOkTypes<R> = R extends Result<infer T, unknown> ? T : never
 export type InferErrTypes<R> = R extends Result<unknown, infer E> ? E : never
 
 export type InferAsyncOkTypes<R> = R extends ResultAsync<infer T, unknown> ? T : never
 export type InferAsyncErrTypes<R> = R extends ResultAsync<unknown, infer E> ? E : never
 
+export type InferMaybeAsyncOkTypes<R> = R extends MaybeResultAsync<infer T, unknown> ? T : never
+export type InferMaybeAsyncErrTypes<R> = R extends MaybeResultAsync<unknown, infer E> ? E : never
+
 /**
  * Short circuits on the FIRST Err value that we find
  */

src/result-async.ts

@@ -16,7 +16,10 @@ import {
   InferAsyncErrTypes,
   InferAsyncOkTypes,
   InferErrTypes,
+  InferMaybeAsyncErrTypes,
+  InferMaybeAsyncOkTypes,
   InferOkTypes,
+  MaybeResultAsync,
 } from './_internals/utils'
 
 export class ResultAsync<T, E> implements PromiseLike<Result<T, E>> {
@@ -86,6 +89,35 @@ export class ResultAsync<T, E> implements PromiseLike<Result<T, E>> {
     ) as CombineResultsWithAllErrorsArrayAsync<T>
   }
 
+  static struct<E, T extends Record<string, MaybeResultAsync<unknown, E>>>(
+    record: T,
+  ): StructResultAsync<E, T> {
+    const results = Object.entries(record).reduce<
+      Array<MaybeResultAsync<[string, unknown], unknown>>
+    >((previous, [key, value]) => {
+      previous.push(value.map((result) => [key, result]))
+      return previous
+    }, [])
+
+    return ResultAsync.fromSafePromise(Promise.all(results)).andThen((results) => {
+      const errors = results.filter((result) => result.isErr())
+      if (0 < errors.length) {
+        return errAsync(
+          errors.map((error) => (error as Err<unknown, InferMaybeAsyncErrTypes<T[keyof T]>>).error),
+        )
+      }
+
+      const successes = results as Ok<[string, unknown], unknown>[]
+      return okAsync(
+        successes.reduce<Record<string, unknown>>((previous, result) => {
+          const [key, value] = result.value
+          previous[key] = value
+          return previous
+        }, {}) as { [Key in keyof T]: InferMaybeAsyncOkTypes<T[Key]> },
+      )
+    })
+  }
+
   map<A>(f: (t: T) => A | Promise<A>): ResultAsync<A, E> {
     return new ResultAsync(
       this._promise.then(async (res: Result<T, E>) => {
@@ -259,6 +291,14 @@ export type CombineResultsWithAllErrorsArrayAsync<
   ? TraverseWithAllErrorsAsync<UnwrapAsync<T>>
   : ResultAsync<ExtractOkAsyncTypes<T>, ExtractErrAsyncTypes<T>[number][]>
 
+export type StructResultAsync<
+  E,
+  T extends Record<string, MaybeResultAsync<unknown, E>>
+> = ResultAsync<
+  { [Key in keyof T]: InferMaybeAsyncOkTypes<T[Key]> },
+  Array<InferMaybeAsyncErrTypes<T[keyof T]>>
+>
+
 // Unwraps the inner `Result` from a `ResultAsync` for all elements.
 type UnwrapAsync<T> = IsLiteralArray<T> extends 1
   ? Writable<T> extends [infer H, ...infer Rest]

src/result.ts

@@ -57,6 +57,23 @@ export namespace Result {
   ): CombineResultsWithAllErrorsArray<T> {
     return combineResultListWithAllErrors(resultList) as CombineResultsWithAllErrorsArray<T>
   }
+
+  export function struct<E, T extends Record<string, Result<unknown, E>>>(
+    record: T,
+  ): StructResult<E, T> {
+    const errors = Object.values(record).filter((result) => result.isErr())
+    if (0 < errors.length) {
+      return err(errors.map((error) => (error as Err<unknown, InferErrTypes<T[keyof T]>>).error))
+    }
+
+    const successes = Object.entries(record) as [string, Ok<T[keyof T], unknown>][]
+    return ok(
+      successes.reduce<Record<string, unknown>>((previous, [key, result]) => {
+        previous[key] = result.value
+        return previous
+      }, {}) as { [Key in keyof T]: InferOkTypes<T[Key]> },
+    )
+  }
 }
 
 export type Result<T, E> = Ok<T, E> | Err<T, E>
@@ -697,4 +714,9 @@ export type CombineResultsWithAllErrorsArray<
   ? TraverseWithAllErrors<T>
   : Result<ExtractOkTypes<T>, ExtractErrTypes<T>[number][]>
 
+export type StructResult<E, T extends Record<string, Result<unknown, E>>> = Result<
+  { [Key in keyof T]: InferOkTypes<T[Key]> },
+  Array<InferErrTypes<T[keyof T]>>
+>
+
 //#endregion

tests/index.test.ts

@@ -738,6 +738,104 @@ describe('Utils', () => {
       })
     })
   })
+  describe('`Result.struct`', () => {
+    it('returns Ok with all values when all results are Ok', () => {
+      const input = {
+        a: ok(1),
+        b: ok('test'),
+        c: ok(true),
+      }
+
+      const result = Result.struct(input)
+
+      expect(result.isOk()).toBe(true)
+      expect(result._unsafeUnwrap()).toEqual({ a: 1, b: 'test', c: true })
+    })
+
+    it('returns Err with a single error when one result is Err', () => {
+      const input = {
+        a: ok(1),
+        b: err('error1'),
+        c: ok(true),
+      }
+
+      const result = Result.struct(input)
+
+      expect(result.isErr()).toBe(true)
+      expect(result._unsafeUnwrapErr()).toEqual(['error1'])
+    })
+
+    it('returns Err with all errors when some results are Err', () => {
+      const input = {
+        a: ok(1),
+        b: err('error1'),
+        c: err('error2'),
+      }
+
+      const result = Result.struct(input)
+
+      expect(result.isErr()).toBe(true)
+      expect(result._unsafeUnwrapErr()).toEqual(['error1', 'error2'])
+    })
+
+    it('returns Ok with an empty object when input is an empty object', () => {
+      const input = {}
+
+      const result = Result.struct(input)
+
+      expect(result.isOk()).toBe(true)
+      expect(result.unwrapOr({})).toEqual({})
+    })
+  })
+  describe('`ResultAsync.struct`', () => {
+    it('returns Ok with all values when all results are Ok', async () => {
+      const input = {
+        a: okAsync(1),
+        b: okAsync('test'),
+        c: okAsync(true),
+      }
+
+      const result = await ResultAsync.struct(input)
+
+      expect(result.isOk()).toBe(true)
+      expect(result._unsafeUnwrap()).toEqual({ a: 1, b: 'test', c: true })
+    })
+
+    it('returns Err with a single error when one result is Err', async () => {
+      const input = {
+        a: okAsync(1),
+        b: errAsync('error1'),
+        c: okAsync(true),
+      }
+
+      const result = await ResultAsync.struct(input)
+
+      expect(result.isErr()).toBe(true)
+      expect(result._unsafeUnwrapErr()).toEqual(['error1'])
+    })
+
+    it('returns Err with all errors when some results are Err', async () => {
+      const input = {
+        a: okAsync(1),
+        b: errAsync('error1'),
+        c: errAsync('error2'),
+      }
+
+      const result = await ResultAsync.struct(input)
+
+      expect(result.isErr()).toBe(true)
+      expect(result._unsafeUnwrapErr()).toEqual(['error1', 'error2'])
+    })
+
+    it('returns Ok with an empty object when input is an empty object', async () => {
+      const input = {}
+
+      const result = await ResultAsync.struct(input)
+
+      expect(result.isOk()).toBe(true)
+      expect(result.unwrapOr({})).toEqual({})
+    })
+  })
 })
 
 describe('ResultAsync', () => {