# Result API Surface

These are ALL available methods for Result. Do not use any method not listed here.

## Types

```typescript
type Result<T, E> = Ok<T> | Err<E>
type ResultPromise<T, E> = Promise<Result<T, E>>
type OkPromise<T> = Promise<Ok<T>>
type ErrPromise<E> = Promise<Err<E>>
type ResultPartitionResult<T, E> = { values: T[]; errors: E[] }
```

## Factory Functions

```typescript
function ok<T>(value: T): Ok<T>
function err<E>(error: E): Err<E>
```

## Ok<T> Instance Methods

```typescript
class Ok<T> {
  readonly value: T

  isOk(): this is Ok<T>
  isErr(): this is never

  map<U>(fn: (value: T) => U): Ok<U>
  mapErr<F>(fn: (error: never) => F): Ok<T>

  flatMap<R extends Result<any, any>>(fn: (value: T) => R): R
  flatMapErr(): this

  match<U>(onOk: (value: T) => U, onErr: (error: never) => U): U

  // Overload 1: type-narrowing predicate
  filter<U extends T, F>(predicate: (value: T) => value is U, errorFactory: (value: T) => F): Ok<U> | Err<F>
  // Overload 2: boolean predicate
  filter<F>(predicate: (value: T) => boolean, errorFactory: (value: T) => F): Ok<T> | Err<F>

  toNullable(): T
  toUndefined(): T
  toString(): string
}
```

## Err<E> Instance Methods

```typescript
class Err<E> {
  readonly err: E

  isOk(): this is never
  isErr(): this is Err<E>

  map<U>(): Err<E>
  mapErr<F>(fn: (error: E) => F): Err<F>

  flatMap(): this
  flatMapErr<R extends Result<any, any>>(fn: (error: E) => R): R

  match<U>(onOk: (value: never) => U, onErr: (error: E) => U): U

  filter(): Err<E>

  toNullable(): null
  toUndefined(): undefined
  toString(): string
}
```

## Result Namespace (Static Methods)

```typescript
Result.from<T, E = unknown>(fn: () => T, errorMap?: (error: unknown) => E): Result<T, E>
Result.isResult<T, E>(value: unknown): value is Result<T, E>
Result.all<T>(results: Ok<T>[]): Ok<T[]>
Result.all<T, E>(results: Result<T, E>[]): Result<T[], E>
Result.partition<T, E>(results: Result<T, E>[]): ResultPartitionResult<T, E>
Result.compact<T, E>(results: Result<T, E>[]): T[]
Result.some<T, E>(results: Result<T, E>[]): boolean
Result.every<T, E>(results: Result<T, E>[]): boolean
```

## ResultPromise Namespace (Async Methods)

```typescript
ResultPromise.from<T, E = unknown>(fn: () => Promise<T>, errorMap?: (error: unknown) => E): ResultPromise<T, E>
ResultPromise.all<T>(promises: Promise<Ok<T>>[]): Promise<Ok<T[]>>
ResultPromise.all<T, E>(promises: Promise<Result<T, E>>[]): Promise<Result<T[], E>>
ResultPromise.partition<T, E>(promises: Promise<Result<T, E>>[]): Promise<ResultPartitionResult<T, E>>
ResultPromise.compact<T, E>(promises: Promise<Result<T, E>>[]): Promise<T[]>
ResultPromise.some<T, E>(promises: Promise<Result<T, E>>[]): Promise<boolean>
ResultPromise.every<T, E>(promises: Promise<Result<T, E>>[]): Promise<boolean>
```