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import { Option } from './Option'
import { ResultAsync } from './ResultAsync'
import { CombineOks, CombineOksObject, FlattenResult, MaybePromise, ResultErrType, ResultLike } from './types'
import { display } from './utils'
/**
* A class representing a value that is either a success (`Ok`) with a value of type `T` or a failure (`Err`) with an error of type `E`.
* Useful for handling operations that may fail in a type-safe way.
*
* @template T The type of the success value.
* @template E The type of the error value.
*/
class Result<T, E> {
private constructor(
private readonly isOkFlag: boolean,
/**
* The success value. Present (`T`) when the `Result` is `Ok`, `undefined` when `Err`.
* Prefer narrowing with {@link Result.isOk} (which refines this to `T`) or
* {@link Result.match}/{@link Result.unwrapOr} over reading it directly.
*/
readonly value?: T,
/**
* The error value. Present (`E`) when the `Result` is `Err`, `undefined` when `Ok`.
* Prefer narrowing with {@link Result.isErr} (which refines this to `E`).
*/
readonly error?: E
) {}
/**
* Creates a `Result` representing a successful outcome (`Ok`) with a value.
*
* @template T The type of the success value.
* @template E The type of the potential error.
* @param value The value to wrap in an `Ok` Result.
* @returns A `Result` containing the provided value as `Ok`.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.isOk()); // true
* console.log(ok.unwrapOr(0)); // 42
*/
static ok<T, E>(value: T): Result<T, E> {
return new Result<T, E>(true, value, undefined)
}
/**
* Creates a `Result` representing a failed outcome (`Err`) with an error.
*
* @template T The type of the potential success value.
* @template E The type of the error.
* @param error The error to wrap in an `Err` Result.
* @returns A `Result` containing the provided error as `Err`.
*
* @example
* const err = Result.err<number, string>("Failed");
* console.log(err.isErr()); // true
* console.log(err.unwrapOr(0)); // 0
*/
static err<T, E>(error: E): Result<T, E> {
return new Result<T, E>(false, undefined, error)
}
/**
* Creates a `Result` from a potentially null or undefined value.
* Returns `Ok` if the value is neither null nor undefined, otherwise `Err` with the provided error.
*
* @template T The type of the success value.
* @template E The type of the error.
* @param value The value to convert to a `Result`.
* @param error The error to use if the value is null or undefined.
* @returns A `Result` containing the value as `Ok` or the error as `Err`.
*
* @example
* const ok = Result.from(42, "Value missing"); // Ok(42)
* const err = Result.from(null, "Value missing"); // Err("Value missing")
* const undefinedErr = Result.from(undefined, "Value missing"); // Err("Value missing")
*/
static from<T, E>(value: T | null | undefined, error: E): Result<T, E> {
return value == null ? new Result<T, E>(false, undefined, error) : new Result<T, E>(true, value, undefined)
}
/**
* Creates a `Result` or `ResultAsync` by executing a function and catching any errors.
* Returns `Ok` with the result if the function succeeds, or `Err` with the mapped error if it throws.
* Handles both synchronous and asynchronous functions.
*
* @template T The type of the success value.
* @template E The type of the error.
* @param fn The function to execute, which may return a value or Promise.
* @param onError The function to map any caught error to the error type `E`.
* @returns A `Result<T, E>` for synchronous functions or `ResultAsync<T, E>` for asynchronous functions.
*
* @example
* // Synchronous function
* const safeParse = Result.try(() => JSON.parse('{"key": "value"}'), e => `Parse error: ${e}`);
* console.log(safeParse.unwrapOr({})); // { key: "value" }
*
* const failedParse = Result.try(() => JSON.parse('invalid'), e => `Parse error: ${e}`);
* console.log(failedParse.unwrapOr({})); // {}
*
* // Asynchronous function
* const asyncFetch = Result.try(
* () => fetch('https://api.example.com/data').then(res => res.json()),
* e => `Fetch error: ${e}`
* );
* const data = await asyncFetch.unwrapOr({ error: "Failed to fetch" });
*/
static try<T, E>(fn: () => T, onError: (e: unknown) => E): Result<T, E>
static try<T, E>(fn: () => Promise<T>, onError: (e: unknown) => E): ResultAsync<T, E>
static try<T, E>(fn: () => MaybePromise<T>, onError: (e: unknown) => E): Result<T, E> | ResultAsync<T, E> {
try {
const result = fn()
if (result instanceof Promise) {
return ResultAsync.try(() => result, onError) // Treat as async
}
return new Result<T, E>(true, result, undefined)
} catch (e) {
return new Result<T, E>(false, undefined, onError(e))
}
}
/**
* Wraps a throwing function into a reusable safe version that returns a `Result` instead of
* throwing. Unlike {@link Result.try} (one-shot), this returns a new function you can call
* many times.
*
* @template A The argument types of the function.
* @template T The success type.
* @template E The error type.
* @param fn The (synchronous) function that may throw.
* @param onError Maps a thrown value to the error type `E`.
* @returns A function with the same arguments that returns `Result<T, E>`.
*
* @example
* const safeParse = Result.fromThrowable(JSON.parse, (e) => `bad json: ${e}`);
* safeParse('{"a":1}'); // Ok({ a: 1 })
* safeParse('nope'); // Err('bad json: ...')
*/
static fromThrowable<A extends readonly unknown[], T, E>(
fn: (...args: A) => T,
onError: (e: unknown) => E
): (...args: A) => Result<T, E> {
return (...args: A) => Result.try(() => fn(...args), onError) as Result<T, E>
}
/**
* Combines an array of `Result`s into a single `Result` of an array.
* Returns the first `Err` encountered, otherwise `Ok` with every value in order.
*
* @template T The type of the success values.
* @template E The type of the error values.
* @param results The array of `Result`s to combine.
* @returns `Ok` with all values, or the first `Err`.
*
* Accepts either a tuple/array of `Result`s (tuple element types are preserved) or a record
* of `Result`s keyed by name.
*
* @example
* // Tuple — positional types preserved:
* Result.combine([Result.ok(1), Result.ok('a')]); // Result<[number, string], never>
* // Record — keys preserved:
* Result.combine({ id: Result.ok(1), name: Result.ok('a') }); // Result<{ id: number; name: string }, never>
* // First Err short-circuits:
* Result.combine([Result.ok<number, string>(1), Result.err<number, string>('x')]); // Err('x')
*/
static combine<T extends readonly Result<unknown, unknown>[] | []>(
results: T
): Result<CombineOks<T>, ResultErrType<T[number]>>
static combine<T extends Record<string, Result<unknown, unknown>>>(
results: T
): Result<CombineOksObject<T>, ResultErrType<T[keyof T]>>
static combine(
results: ReadonlyArray<Result<unknown, unknown>> | Record<string, Result<unknown, unknown>>
): Result<unknown, unknown> {
if (Array.isArray(results)) {
const values: unknown[] = []
for (const result of results) {
if (result.isErr()) return new Result(false, undefined, result.error)
values.push(result.value)
}
return new Result(true, values, undefined)
}
const out: Record<string, unknown> = {}
for (const key of Object.keys(results)) {
const result = (results as Record<string, Result<unknown, unknown>>)[key]
if (result.isErr()) return new Result(false, undefined, result.error)
out[key] = result.value
}
return new Result(true, out, undefined)
}
/**
* Like {@link Result.combine}, but accumulates every `Err` instead of stopping at the first.
* Returns `Ok` with all values when every `Result` is `Ok`, otherwise `Err` with all errors.
*
* @template T The type of the success values.
* @template E The type of the error values.
* @param results The array of `Result`s to combine.
* @returns `Ok` with all values, or `Err` with an array of all errors.
*
* Accepts a tuple/array or a record of `Result`s, mirroring {@link Result.combine}.
*
* @example
* const r = Result.combineWithAllErrors([Result.ok<number, string>(1), Result.err<number, string>('a'), Result.err<number, string>('b')]);
* console.log(r.match({ ok: () => [], err: (e) => e })); // ['a', 'b']
*/
static combineWithAllErrors<T extends readonly Result<unknown, unknown>[] | []>(
results: T
): Result<CombineOks<T>, ResultErrType<T[number]>[]>
static combineWithAllErrors<T extends Record<string, Result<unknown, unknown>>>(
results: T
): Result<CombineOksObject<T>, ResultErrType<T[keyof T]>[]>
static combineWithAllErrors(
results: ReadonlyArray<Result<unknown, unknown>> | Record<string, Result<unknown, unknown>>
): Result<unknown, unknown[]> {
const errors: unknown[] = []
if (Array.isArray(results)) {
const arr = results as ReadonlyArray<Result<unknown, unknown>>
const values: unknown[] = []
for (const result of arr) {
result.match({ ok: (v) => void values.push(v), err: (e) => void errors.push(e) })
}
return errors.length > 0
? new Result<unknown, unknown[]>(false, undefined, errors)
: new Result<unknown, unknown[]>(true, values, undefined)
}
const out: Record<string, unknown> = {}
for (const key of Object.keys(results)) {
;(results as Record<string, Result<unknown, unknown>>)[key].match({
ok: (v) => void (out[key] = v),
err: (e) => void errors.push(e),
})
}
return errors.length > 0
? new Result<unknown, unknown[]>(false, undefined, errors)
: new Result<unknown, unknown[]>(true, out, undefined)
}
/**
* Checks if the `Result` is `Ok` (contains a value).
*
* @returns `true` if the `Result` is `Ok`, `false` if it is `Err`.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.isOk()); // true
*
* const err = Result.err<number, string>("Failed");
* console.log(err.isOk()); // false
*/
isOk(): this is Result<T, E> & { readonly value: T } {
return this.isOkFlag
}
/**
* Checks if the `Result` is `Err` (contains an error).
*
* @returns `true` if the `Result` is `Err`, `false` if it is `Ok`.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.isErr()); // false
*
* const err = Result.err<number, string>("Failed");
* console.log(err.isErr()); // true
*/
isErr(): this is Result<T, E> & { readonly error: E } {
return !this.isOkFlag
}
/**
* Checks if the `Result` is `Ok` and contains a specific value.
*
* @param value The value to compare against.
* @returns `true` if the `Result` is `Ok` and its value equals the provided value, `false` otherwise.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.contains(42)); // true
* console.log(ok.contains(43)); // false
*
* const err = Result.err<number, string>("Failed");
* console.log(err.contains(42)); // false
*/
contains(value: T): boolean {
return this.isOkFlag && this.value === value
}
/**
* Transforms the value in an `Ok` `Result` using the provided function.
* Returns the original `Err` if the `Result` is `Err`.
*
* @template U The type of the transformed value.
* @param fn The function to transform the value.
* @returns A `Result` containing the transformed value or the original error.
*
* @example
* const ok = Result.ok<number, string>(42);
* const mapped = ok.map(x => x * 2);
* console.log(mapped.unwrapOr(0)); // 84
*
* const err = Result.err<number, string>("Failed");
* console.log(err.map(x => x * 2).unwrapOr(0)); // 0
*/
map<U>(fn: (value: T) => Promise<U>): ResultAsync<U, E>
map<U>(fn: (value: T) => U): Result<U, E>
map<U>(fn: (value: T) => MaybePromise<U>): Result<U, E> | ResultAsync<U, E> {
if (!this.isOkFlag) return new Result<U, E>(false, undefined, this.error)
const out = fn(this.value!)
return out instanceof Promise
? ResultAsync._fromPromise(out.then((v) => Result.ok<U, E>(v)))
: new Result<U, E>(true, out, undefined)
}
/**
* Transforms the error in an `Err` `Result` using the provided function.
* Returns the original `Ok` if the `Result` is `Ok`.
*
* @template F The type of the transformed error.
* @param fn The function to transform the error.
* @returns A `Result` containing the original value or the transformed error.
*
* @example
* const err = Result.err<number, string>("Failed");
* const mappedErr = err.mapErr(e => `Error: ${e}`);
* console.log(mappedErr.unwrapOrElse(e => e)); // "Error: Failed"
*
* const ok = Result.ok<number, string>(42);
* console.log(ok.mapErr(e => `Error: ${e}`).unwrapOr(0)); // 42
*/
mapErr<F>(fn: (error: E) => Promise<F>): ResultAsync<T, F>
mapErr<F>(fn: (error: E) => F): Result<T, F>
mapErr<F>(fn: (error: E) => MaybePromise<F>): Result<T, F> | ResultAsync<T, F> {
if (this.isOkFlag) return new Result<T, F>(true, this.value, undefined)
const out = fn(this.error!)
return out instanceof Promise
? ResultAsync._fromPromise(out.then((e) => Result.err<T, F>(e)))
: new Result<T, F>(false, undefined, out)
}
/**
* Chains a `Result` by applying a function that returns another `Result`.
* Returns the original `Err` if the `Result` is `Err`.
*
* @template U The type of the value in the resulting `Result`.
* @template F The type of the error in the resulting `Result`.
* @param fn The function that returns a `Result`.
* @returns A `Result` containing the result of the function or the original error.
*
* @example
* const ok = Result.ok<number, string>(42);
* const chained = ok.andThen(x => Result.ok<string, string>(`Value: ${x}`));
* console.log(chained.unwrapOr("None")); // "Value: 42"
*
* const err = Result.err<number, string>("Failed");
* console.log(err.andThen(x => Result.ok<string, string>(`Value: ${x}`)).unwrapOr("None")); // "None"
*/
andThen<U, F>(fn: (value: T) => ResultAsync<U, F> | Promise<Result<U, F>>): ResultAsync<U, E | F>
andThen<U, F>(fn: (value: T) => Result<U, F>): Result<U, E | F>
andThen<U, F>(fn: (value: T) => ResultLike<U, F>): Result<U, E | F> | ResultAsync<U, E | F> {
if (!this.isOkFlag) return new Result<U, E | F>(false, undefined, this.error)
const next = fn(this.value!)
if (next instanceof ResultAsync) return next as ResultAsync<U, E | F>
if (next instanceof Promise) return ResultAsync._fromPromise(next as Promise<Result<U, E | F>>)
return next as Result<U, E | F>
}
/**
* Returns the current `Result` if it is `Ok`, otherwise returns the result of the provided function.
*
* @template F The type of the error in the fallback `Result`.
* @param fn The function returning a `Result` as a fallback.
* @returns A `Result` containing the original value or the fallback result.
*
* @example
* const err = Result.err<number, string>("Failed");
* const fallback = err.orElse(e => Result.ok<number, string>(0));
* console.log(fallback.unwrapOr(-1)); // 0
*
* const ok = Result.ok<number, string>(42);
* console.log(ok.orElse(e => Result.ok<number, string>(0)).unwrapOr(-1)); // 42
*/
orElse<F>(fn: (error: E) => Result<T, F>): Result<T, E | F>
orElse<F>(fn: (error: E) => ResultAsync<T, F> | Promise<Result<T, F>>): ResultAsync<T, E | F>
orElse<F>(fn: (error: E) => ResultLike<T, F>): Result<T, E | F> | ResultAsync<T, E | F> {
if (this.isOkFlag) return new Result<T, E | F>(true, this.value!, undefined)
const next = fn(this.error!)
if (next instanceof ResultAsync) return next as ResultAsync<T, E | F>
if (next instanceof Promise) return ResultAsync._fromPromise(next as Promise<Result<T, E | F>>)
return next as Result<T, E | F>
}
/**
* Filters the `Result` based on a predicate. Returns the original `Ok` if the predicate is true, otherwise `Err` with the provided error.
*
* @param predicate The function to test the value.
* @param error The error to use if the predicate fails.
* @returns The original `Result` if the predicate passes, otherwise `Err` with the provided error.
*
* @example
* const ok = Result.ok<number, string>(42);
* const filtered = ok.filter(x => x > 40, "Too small");
* console.log(filtered.unwrapOr(0)); // 42
*
* const failedFilter = ok.filter(x => x < 40, "Too small");
* console.log(failedFilter.unwrapOr(0)); // 0
*
* const err = Result.err<number, string>("Failed");
* console.log(err.filter(x => x > 40, "Too small").unwrapOr(0)); // 0
*/
filter(predicate: (value: T) => Promise<boolean>, error: MaybePromise<E>): ResultAsync<T, E>
filter(predicate: (value: T) => boolean, error: E): Result<T, E>
filter(
predicate: (value: T) => MaybePromise<boolean>,
error: MaybePromise<E>
): Result<T, E> | ResultAsync<T, E> {
if (!this.isOkFlag) return this
const verdict = predicate(this.value!)
if (verdict instanceof Promise) {
return ResultAsync._fromPromise(
verdict.then(async (ok) => (ok ? (this as Result<T, E>) : Result.err<T, E>(await Promise.resolve(error))))
)
}
return verdict ? this : new Result<T, E>(false, undefined, error as E)
}
/**
* Combines two `Result`s into a single `Result` containing a tuple of their values.
* Returns `Err` if either `Result` is `Err`.
*
* @template U The type of the value in the other `Result`.
* @template F The type of the error in the other `Result`.
* @param other The other `Result` to combine with.
* @returns A `Result` containing a tuple of values or the first error encountered.
*
* @example
* const ok1 = Result.ok<number, string>(42);
* const ok2 = Result.ok<string, string>("hello");
* const zipped = ok1.zip(ok2);
* console.log(zipped.unwrapOr([0, ""])); // [42, "hello"]
*
* const err = Result.err<string, string>("Failed");
* console.log(ok1.zip(err).unwrapOr([0, ""])); // [0, ""]
*/
zip<U, F>(other: ResultAsync<U, F> | Promise<Result<U, F>>): ResultAsync<[T, U], E | F>
zip<U, F>(other: Result<U, F>): Result<[T, U], E | F>
zip<U, F>(other: ResultLike<U, F>): Result<[T, U], E | F> | ResultAsync<[T, U], E | F> {
if (other instanceof ResultAsync) return this.toAsync().zip(other)
if (other instanceof Promise) return this.toAsync().zip(ResultAsync._fromPromise(other))
return this.match({
ok: (value1) =>
other.match({
ok: (value2) => Result.ok<[T, U], E | F>([value1, value2]),
err: (error) => Result.err<[T, U], E | F>(error),
}),
err: (error) => Result.err<[T, U], E | F>(error),
})
}
/**
* Flattens a nested `Result` into a single `Result`.
* If the `Result` is `Ok` and contains another `Result`, it recursively flattens it.
*
* Nested errors are preserved: flattening a `Result<Result<T, F>, E>` yields `Result<T, E | F>`.
*
* @returns A flattened `Result`.
*
* @example
* const nested = Result.ok<Result<number, string>, string>(Result.ok<number, string>(42));
* console.log(nested.flatten().unwrapOr(0)); // 42
*
* const ok = Result.ok<number, string>(42);
* console.log(ok.flatten().unwrapOr(0)); // 42
*
* const err = Result.err<number, string>("Failed");
* console.log(err.flatten().unwrapOr(0)); // 0
*/
flatten(): FlattenResult<T, E> {
if (!this.isOkFlag) return new Result<unknown, E>(false, undefined, this.error) as FlattenResult<T, E>
const inner = this.value
return (inner instanceof Result ? inner.flatten() : new Result<unknown, E>(true, inner, undefined)) as FlattenResult<
T,
E
>
}
/**
* Returns the value if the `Result` is `Ok`, otherwise returns the provided default value.
*
* @param defaultValue The value to return if the `Result` is `Err`.
* @returns The value of `Ok` or the default value.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.unwrapOr(0)); // 42
*
* const err = Result.err<number, string>("Failed");
* console.log(err.unwrapOr(0)); // 0
*/
unwrapOr(defaultValue: T): T {
return this.isOkFlag ? this.value! : defaultValue
}
/**
* Returns the value if the `Result` is `Ok`, otherwise returns the result of the provided function.
*
* @param fn The function to compute the default value based on the error.
* @returns The value of `Ok` or the computed default value.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.unwrapOrElse(e => 0)); // 42
*
* const err = Result.err<number, string>("Failed");
* console.log(err.unwrapOrElse(e => e.length)); // 6
*/
unwrapOrElse(fn: (error: E) => T): T {
return this.isOkFlag ? this.value! : fn(this.error!)
}
/**
* Applies `fn` to the `Ok` value, or returns `defaultValue` if `Err` — in one step.
*
* @template U The result type.
* @param defaultValue The value to return when `Err`.
* @param fn Maps the `Ok` value to `U`.
*
* @example
* Result.ok<number, string>(2).mapOr(0, (x) => x * 10); // 20
* Result.err<number, string>('e').mapOr(0, (x) => x * 10); // 0
*/
mapOr<U>(defaultValue: U, fn: (value: T) => U): U {
return this.isOkFlag ? fn(this.value!) : defaultValue
}
/**
* Applies `fn` to the `Ok` value, or `onError` to the error if `Err` — in one step.
*
* @template U The result type.
* @param onError Maps the error to `U` when `Err`.
* @param fn Maps the `Ok` value to `U`.
*
* @example
* Result.err<number, string>('boom').mapOrElse((e) => e.length, (x) => x * 10); // 4
*/
mapOrElse<U>(onError: (error: E) => U, fn: (value: T) => U): U {
return this.isOkFlag ? fn(this.value!) : onError(this.error!)
}
/**
* Unsafe escape hatch: returns the `Ok` value, or throws if the `Result` is `Err`.
* Prefer {@link Result.unwrapOr}/{@link Result.match} in production code.
*
* @returns The contained `Ok` value.
* @throws If the `Result` is `Err`.
*
* @example
* console.log(Result.ok(42).unwrap()); // 42
* Result.err('boom').unwrap(); // throws
*/
unwrap(): T {
if (this.isOkFlag) return this.value!
throw new Error(`Called unwrap() on an Err value: ${String(this.error)}`)
}
/**
* Unsafe escape hatch: returns the `Err` value, or throws if the `Result` is `Ok`.
*
* @returns The contained `Err` value.
* @throws If the `Result` is `Ok`.
*
* @example
* console.log(Result.err('boom').unwrapErr()); // "boom"
* Result.ok(42).unwrapErr(); // throws
*/
unwrapErr(): E {
if (!this.isOkFlag) return this.error!
throw new Error(`Called unwrapErr() on an Ok value: ${String(this.value)}`)
}
/**
* Unsafe escape hatch: returns the `Ok` value, or throws an `Error` with `message` if `Err`.
*
* @param message The error message to throw with when the `Result` is `Err`.
* @returns The contained `Ok` value.
* @throws If the `Result` is `Err`.
*
* @example
* console.log(Result.ok(42).expect('must have a value')); // 42
*/
expect(message: string): T {
if (this.isOkFlag) return this.value!
throw new Error(message)
}
/**
* Unsafe escape hatch: returns the `Err` value, or throws an `Error` with `message` if `Ok`.
*
* @param message The error message to throw with when the `Result` is `Ok`.
* @returns The contained `Err` value.
* @throws If the `Result` is `Ok`.
*
* @example
* console.log(Result.err('boom').expectErr('must be an error')); // "boom"
*/
expectErr(message: string): E {
if (!this.isOkFlag) return this.error!
throw new Error(message)
}
/**
* Pattern-matches the `Result`, executing the appropriate branch based on whether it is `Ok` or `Err`.
*
* @template U The type of the result.
* @param branches An object with `ok` and `err` branches.
* @returns The result of the executed branch.
*
* @example
* const ok = Result.ok<number, string>(42);
* const result = ok.match({
* ok: x => `Value: ${x}`,
* err: e => `Error: ${e}`,
* });
* console.log(result); // "Value: 42"
*
* const err = Result.err<number, string>("Failed");
* console.log(err.match({
* ok: x => `Value: ${x}`,
* err: e => `Error: ${e}`,
* })); // "Error: Failed"
*/
match<U>(branches: { ok: (value: T) => U; err: (error: E) => U }): U {
return this.isOkFlag ? branches.ok(this.value!) : branches.err(this.error!)
}
/**
* Converts the `Result` to an `Option`, discarding the error.
* Returns `Some` if the `Result` is `Ok`, otherwise `None`.
*
* @returns An `Option` containing the value or `None`.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(ok.toOption().unwrapOr(0)); // 42
*
* const err = Result.err<number, string>("Failed");
* console.log(err.toOption().unwrapOr(0)); // 0
*/
toOption(): Option<T> {
return this.isOkFlag ? Option.some(this.value!) : Option.none()
}
/**
* Recovers from an `Err` `Result` by providing a fallback value.
* Returns the original `Ok` if the `Result` is `Ok`.
*
* @param fn The function to compute the recovery value based on the error.
* @returns A `Result` containing the original value or the recovery value.
*
* @example
* const err = Result.err<number, string>("Failed");
* const recovered = err.recover(e => e.length);
* console.log(recovered.unwrapOr(0)); // 6
*
* const ok = Result.ok<number, string>(42);
* console.log(ok.recover(e => e.length).unwrapOr(0)); // 42
*/
recover(fn: (error: E) => Promise<T>): ResultAsync<T, E>
recover(fn: (error: E) => T): Result<T, E>
recover(fn: (error: E) => MaybePromise<T>): Result<T, E> | ResultAsync<T, E> {
if (this.isOkFlag) return this
const out = fn(this.error!)
return out instanceof Promise
? ResultAsync._fromPromise(out.then((v) => Result.ok<T, E>(v)))
: new Result<T, E>(true, out, undefined)
}
/**
* Converts the `Result` to a `Result` containing an array.
* If `Ok`, wraps the value in an array (or keeps it if already an array); if `Err`, returns an empty array.
*
* @returns A `Result` containing an array of values or the original error.
*
* @example
* const ok = Result.ok<number, string>(42);
* const sequenced = ok.sequence();
* console.log(sequenced.unwrapOr([])); // [42]
*
* const arrayOk = Result.ok<number[], string>([1, 2, 3]);
* console.log(arrayOk.sequence().unwrapOr([])); // [1, 2, 3]
*
* const err = Result.err<number, string>("Failed");
* console.log(err.sequence().unwrapOr([])); // []
*/
sequence(): Result<T[], E> {
if (this.isOkFlag) {
return new Result<T[], E>(true, Array.isArray(this.value) ? [...this.value] : [this.value!], undefined)
}
return new Result<T[], E>(false, undefined, this.error!)
}
/**
* Performs a side effect with the value if the `Result` is `Ok`.
* Returns the original `Result` unchanged.
*
* @param fn The function to execute with the value.
* @returns The original `Result`.
*
* @example
* const ok = Result.ok<number, string>(42);
* const tapped = ok.tap(x => console.log(`Value: ${x}`));
* console.log(tapped.unwrapOr(0)); // Logs "Value: 42", returns 42
*
* const err = Result.err<number, string>("Failed");
* err.tap(x => console.log(`Value: ${x}`)); // No log
*/
tap(fn: (value: T) => Promise<void>): ResultAsync<T, E>
tap(fn: (value: T) => void): Result<T, E>
tap(fn: (value: T) => MaybePromise<void>): Result<T, E> | ResultAsync<T, E> {
if (!this.isOkFlag) return this
const out = fn(this.value!)
return out instanceof Promise
? ResultAsync._fromPromise(out.then(() => this as Result<T, E>))
: this
}
/**
* Performs a side effect with the error if the `Result` is `Err`.
* Returns the original `Result` unchanged.
*
* @param fn The function to execute with the error.
* @returns The original `Result`.
*
* @example
* const err = Result.err<number, string>("Failed");
* const tapped = err.tapErr(e => console.log(`Error: ${e}`));
* console.log(tapped.unwrapOr(0)); // Logs "Error: Failed", returns 0
*
* const ok = Result.ok<number, string>(42);
* ok.tapErr(e => console.log(`Error: ${e}`)); // No log
*/
tapErr(fn: (error: E) => Promise<void>): ResultAsync<T, E>
tapErr(fn: (error: E) => void): Result<T, E>
tapErr(fn: (error: E) => MaybePromise<void>): Result<T, E> | ResultAsync<T, E> {
if (this.isOkFlag) return this
const out = fn(this.error!)
return out instanceof Promise
? ResultAsync._fromPromise(out.then(() => this as Result<T, E>))
: this
}
/**
* Converts the `Result` to a `ResultAsync`, enabling asynchronous operations.
*
* @returns A `ResultAsync` containing the value or error.
*
* @example
* const ok = Result.ok<number, string>(42);
* const asyncOk = ok.toAsync();
* console.log(await asyncOk.unwrapOr(0)); // 42
*
* const err = Result.err<number, string>("Failed");
* const asyncErr = err.toAsync();
* console.log(await asyncErr.unwrapOr(0)); // 0
*/
toAsync(): ResultAsync<T, E> {
return this.match({
ok: (value) => ResultAsync.ok<T, E>(value),
err: (error) => ResultAsync.err<T, E>(error),
})
}
/** Alias for {@link Result.tap} (Rust-style naming). */
inspect(fn: (value: T) => Promise<void>): ResultAsync<T, E>
inspect(fn: (value: T) => void): Result<T, E>
inspect(fn: (value: T) => MaybePromise<void>): Result<T, E> | ResultAsync<T, E> {
if (!this.isOkFlag) return this
const out = fn(this.value!)
return out instanceof Promise ? ResultAsync._fromPromise(out.then(() => this as Result<T, E>)) : this
}
/** Alias for {@link Result.tapErr} (Rust-style naming). */
inspectErr(fn: (error: E) => Promise<void>): ResultAsync<T, E>
inspectErr(fn: (error: E) => void): Result<T, E>
inspectErr(fn: (error: E) => MaybePromise<void>): Result<T, E> | ResultAsync<T, E> {
if (this.isOkFlag) return this
const out = fn(this.error!)
return out instanceof Promise ? ResultAsync._fromPromise(out.then(() => this as Result<T, E>)) : this
}
/**
* Returns a readable representation, e.g. `Ok(42)` or `Err("boom")`.
*/
toString(): string {
return this.isOkFlag ? `Ok(${display(this.value)})` : `Err(${display(this.error)})`
}
/** Node's `util.inspect` hook, so `console.log` prints `Ok(42)` instead of internal fields. */
[Symbol.for('nodejs.util.inspect.custom')](): string {
return this.toString()
}
/** JSON representation: `{ type: 'Ok', value }` or `{ type: 'Err', error }`. */
toJSON(): { type: 'Ok'; value: T } | { type: 'Err'; error: E } {
return this.isOkFlag ? { type: 'Ok', value: this.value! } : { type: 'Err', error: this.error! }
}
}
/**
* Type guard to check if a value is an instance of `Result`.
*
* @template T The type of the success value.
* @template E The type of the error value.
* @param value The value to check.
* @returns `true` if the value is a `Result`, `false` otherwise.
*
* @example
* const ok = Result.ok<number, string>(42);
* console.log(isResult(ok)); // true
* console.log(isResult(42)); // false
* console.log(isResult(Option.some(42))); // false
*/
function isResult<T, E>(value: any): value is Result<T, E> {
return value instanceof Result
}
export { Result, isResult }
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