ResultInterface.php

<?php

declare(strict_types=1);

namespace Psl\Result;

use Closure;
use Psl;
use Throwable;

/**
 * Represents a result of operation that either has a successful result or the throwable object if
 * that operation failed.
 *
 * This is an interface. You get generally `ResultInterface<T>` by calling `wrap<T>()`, passing in
 * the `(Closure(): T)`, and a `Success<T>` or `Failure<Te>` is returned.
 *
 * @template T
 *
 * @extends Psl\Promise\PromiseInterface<T>
 */
interface ResultInterface extends Psl\Promise\PromiseInterface
{
    /**
     * Transforms a promise's value by applying a function to the promise's fulfillment
     * or rejection value.
     *
     * It is a shortcut for:
     *
     * ```php
     * $promise->then($success, $failure);
     * // same as:
     * $promise->map($success)->catch($failure);
     * ```
     *
     * @template Ts
     *
     * @param (Closure(T): Ts) $success
     * @param (Closure(Throwable): Ts) $failure
     *
     * @return ResultInterface<Ts>
     */
    public function then(Closure $success, Closure $failure): ResultInterface;

    /**
     * Attaches a callback that is invoked if this promise is fulfilled.
     *
     * The returned promise is resolved with the return value of the callback,
     * or is rejected with a throwable thrown from the callback.
     *
     * @template Ts
     *
     * @param (Closure(T): Ts) $success
     *
     * @return ResultInterface<Ts>
     */
    public function map(Closure $success): ResultInterface;

    /**
     * Attaches a callback that is invoked if this promise is rejected.
     *
     * The returned promise is resolved with the return value of the callback,
     * or is rejected with a throwable thrown from the callback.
     *
     * @template Ts
     *
     * @param (Closure(Throwable): Ts) $failure
     *
     * @return ResultInterface<T|Ts>
     */
    public function catch(Closure $failure): ResultInterface;

    /**
     * Attaches a callback that is always invoked when the promise is resolved.
     *
     * The returned promise resolves with the same value as this promise once the callback has finished execution.
     *
     * If the callback throws, the returned promise will be rejected with the thrown throwable.
     *
     * @param (Closure(): void) $always
     *
     * @return ResultInterface<T>
     */
    public function always(Closure $always): ResultInterface;

    /**
     * Return the result of the operation, or throw underlying throwable.
     *
     * - if the operation succeeded: return its result.
     * - if the operation failed: throw the throwable inciting failure.
     *
     * @return T - The result of the operation upon success
     *
     * @psalm-mutation-free
     */
    public function getResult();

    /**
     * Return the underlying throwable, or fail with a invariant violation exception.
     *
     * - if the operation succeeded: fails with a invariant violation exception.
     * - if the operation failed: returns the throwable indicating failure.
     *
     * @throws Psl\Exception\InvariantViolationException - When the operation succeeded
     *
     * @psalm-mutation-free
     */
    public function getThrowable(): Throwable;

    /**
     * Indicates whether the operation associated with this wrapper existed normally.
     *
     * if `isSucceeded()` returns `true`, `isFailed()` returns false.
     *
     * @return bool - `true` if the operation succeeded; `false` otherwise
     *
     * @psalm-mutation-free
     */
    public function isSucceeded(): bool;

    /**
     * Indicates whether the operation associated with this wrapper exited abnormally via a throwable of some sort.
     *
     * if `isFailed()` returns `true`, `isSucceeded()` returns false.
     *
     * @return bool - `true` if the operation failed; `false` otherwise
     *
     * @psalm-mutation-free
     */
    public function isFailed(): bool;

    /**
     * Unwrapping and transforming a result can be done by using the proceed method.
     * The implementation will either run the `$on_success` or `$on_failure` callback.
     * The callback will receive the result or Throwable as an argument,
     * so that you can transform it to anything you want.
     *
     * @template Ts
     *
     * @param (Closure(T): Ts) $success
     * @param (Closure(Throwable): Ts) $failure
     *
     * @return Ts
     */
    public function proceed(Closure $success, Closure $failure): mixed;
}