<?php
/*
* Copyright 2012 Johannes M. Schmitt <[email protected]>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
namespace PhpOption;
use ArrayAccess;
use IteratorAggregate;
/**
* @template T
*
* @implements IteratorAggregate<T>
*/
abstract class Option implements IteratorAggregate
{
/**
* Creates an option given a return value.
*
* This is intended for consuming existing APIs and allows you to easily
* convert them to an option. By default, we treat ``null`` as the None
* case, and everything else as Some.
*
* @template S
*
* @param S $value The actual return value.
* @param S $noneValue The value which should be considered "None"; null by
* default.
*
* @return Option<S>
*/
public static function fromValue($value, $noneValue = null)
{
if ($value === $noneValue) {
return None::create();
}
return new Some($value);
}
/**
* Creates an option from an array's value.
*
* If the key does not exist in the array, the array is not actually an
* array, or the array's value at the given key is null, None is returned.
* Otherwise, Some is returned wrapping the value at the given key.
*
* @template S
*
* @param array<string|int,S>|ArrayAccess<string|int,S>|null $array A potential array or \ArrayAccess value.
* @param string $key The key to check.
*
* @return Option<S>
*/
public static function fromArraysValue($array, $key)
{
if (!(is_array($array) || $array instanceof ArrayAccess) || !isset($array[$key])) {
return None::create();
}
return new Some($array[$key]);
}
/**
* Creates a lazy-option with the given callback.
*
* This is also a helper constructor for lazy-consuming existing APIs where
* the return value is not yet an option. By default, we treat ``null`` as
* None case, and everything else as Some.
*
* @template S
*
* @param callable $callback The callback to evaluate.
* @param array $arguments The arguments for the callback.
* @param S $noneValue The value which should be considered "None";
* null by default.
*
* @return LazyOption<S>
*/
public static function fromReturn($callback, array $arguments = [], $noneValue = null)
{
return new LazyOption(static function () use ($callback, $arguments, $noneValue) {
/** @var mixed */
$return = call_user_func_array($callback, $arguments);
if ($return === $noneValue) {
return None::create();
}
return new Some($return);
});
}
/**
* Option factory, which creates new option based on passed value.
*
* If value is already an option, it simply returns. If value is callable,
* LazyOption with passed callback created and returned. If Option
* returned from callback, it returns directly. On other case value passed
* to Option::fromValue() method.
*
* @template S
*
* @param Option<S>|callable|S $value
* @param S $noneValue Used when $value is mixed or
* callable, for None-check.
*
* @return Option<S>|LazyOption<S>
*/
public static function ensure($value, $noneValue = null)
{
if ($value instanceof self) {
return $value;
} elseif (is_callable($value)) {
return new LazyOption(static function () use ($value, $noneValue) {
/** @var mixed */
$return = $value();
if ($return instanceof self) {
return $return;
} else {
return self::fromValue($return, $noneValue);
}
});
} else {
return self::fromValue($value, $noneValue);
}
}
/**
* Lift a function so that it accepts Option as parameters.
*
* We return a new closure that wraps the original callback. If any of the
* parameters passed to the lifted function is empty, the function will
* return a value of None. Otherwise, we will pass all parameters to the
* original callback and return the value inside a new Option, unless an
* Option is returned from the function, in which case, we use that.
*
* @template S
*
* @param callable $callback
* @param mixed $noneValue
*
* @return callable
*/
public static function lift($callback, $noneValue = null)
{
return static function () use ($callback, $noneValue) {
/** @var array<int, mixed> */
$args = func_get_args();
$reduced_args = array_reduce(
$args,
/** @param bool $status */
static function ($status, self $o) {
return $o->isEmpty() ? true : $status;
},
false
);
// if at least one parameter is empty, return None
if ($reduced_args) {
return None::create();
}
$args = array_map(
/** @return T */
static function (self $o) {
// it is safe to do so because the fold above checked
// that all arguments are of type Some
/** @var T */
return $o->get();
},
$args
);
return self::ensure(call_user_func_array($callback, $args), $noneValue);
};
}
/**
* Returns the value if available, or throws an exception otherwise.
*
* @throws \RuntimeException If value is not available.
*
* @return T
*/
abstract public function get();
/**
* Returns the value if available, or the default value if not.
*
* @template S
*
* @param S $default
*
* @return T|S
*/
abstract public function getOrElse($default);
/**
* Returns the value if available, or the results of the callable.
*
* This is preferable over ``getOrElse`` if the computation of the default
* value is expensive.
*
* @template S
*
* @param callable():S $callable
*
* @return T|S
*/
abstract public function getOrCall($callable);
/**
* Returns the value if available, or throws the passed exception.
*
* @param \Exception $ex
*
* @return T
*/
abstract public function getOrThrow(\Exception $ex);
/**
* Returns true if no value is available, false otherwise.
*
* @return bool
*/
abstract public function isEmpty();
/**
* Returns true if a value is available, false otherwise.
*
* @return bool
*/
abstract public function isDefined();
/**
* Returns this option if non-empty, or the passed option otherwise.
*
* This can be used to try multiple alternatives, and is especially useful
* with lazy evaluating options:
*
* ```php
* $repo->findSomething()
* ->orElse(new LazyOption(array($repo, 'findSomethingElse')))
* ->orElse(new LazyOption(array($repo, 'createSomething')));
* ```
*
* @param Option<T> $else
*
* @return Option<T>
*/
abstract public function orElse(self $else);
/**
* This is similar to map() below except that the return value has no meaning;
* the passed callable is simply executed if the option is non-empty, and
* ignored if the option is empty.
*
* In all cases, the return value of the callable is discarded.
*
* ```php
* $comment->getMaybeFile()->ifDefined(function($file) {
* // Do something with $file here.
* });
* ```
*
* If you're looking for something like ``ifEmpty``, you can use ``getOrCall``
* and ``getOrElse`` in these cases.
*
* @deprecated Use forAll() instead.
*
* @param callable(T):mixed $callable
*
* @return void
*/
abstract public function ifDefined($callable);
/**
* This is similar to map() except that the return value of the callable has no meaning.
*
* The passed callable is simply executed if the option is non-empty, and ignored if the
* option is empty. This method is preferred for callables with side-effects, while map()
* is intended for callables without side-effects.
*
* @param callable(T):mixed $callable
*
* @return Option<T>
*/
abstract public function forAll($callable);
/**
* Applies the callable to the value of the option if it is non-empty,
* and returns the return value of the callable wrapped in Some().
*
* If the option is empty, then the callable is not applied.
*
* ```php
* (new Some("foo"))->map('strtoupper')->get(); // "FOO"
* ```
*
* @template S
*
* @param callable(T):S $callable
*
* @return Option<S>
*/
abstract public function map($callable);
/**
* Applies the callable to the value of the option if it is non-empty, and
* returns the return value of the callable directly.
*
* In contrast to ``map``, the return value of the callable is expected to
* be an Option itself; it is not automatically wrapped in Some().
*
* @template S
*
* @param callable(T):Option<S> $callable must return an Option
*
* @return Option<S>
*/
abstract public function flatMap($callable);
/**
* If the option is empty, it is returned immediately without applying the callable.
*
* If the option is non-empty, the callable is applied, and if it returns true,
* the option itself is returned; otherwise, None is returned.
*
* @param callable(T):bool $callable
*
* @return Option<T>
*/
abstract public function filter($callable);
/**
* If the option is empty, it is returned immediately without applying the callable.
*
* If the option is non-empty, the callable is applied, and if it returns false,
* the option itself is returned; otherwise, None is returned.
*
* @param callable(T):bool $callable
*
* @return Option<T>
*/
abstract public function filterNot($callable);
/**
* If the option is empty, it is returned immediately.
*
* If the option is non-empty, and its value does not equal the passed value
* (via a shallow comparison ===), then None is returned. Otherwise, the
* Option is returned.
*
* In other words, this will filter all but the passed value.
*
* @param T $value
*
* @return Option<T>
*/
abstract public function select($value);
/**
* If the option is empty, it is returned immediately.
*
* If the option is non-empty, and its value does equal the passed value (via
* a shallow comparison ===), then None is returned; otherwise, the Option is
* returned.
*
* In other words, this will let all values through except the passed value.
*
* @param T $value
*
* @return Option<T>
*/
abstract public function reject($value);
/**
* Binary operator for the initial value and the option's value.
*
* If empty, the initial value is returned. If non-empty, the callable
* receives the initial value and the option's value as arguments.
*
* ```php
*
* $some = new Some(5);
* $none = None::create();
* $result = $some->foldLeft(1, function($a, $b) { return $a + $b; }); // int(6)
* $result = $none->foldLeft(1, function($a, $b) { return $a + $b; }); // int(1)
*
* // This can be used instead of something like the following:
* $option = Option::fromValue($integerOrNull);
* $result = 1;
* if ( ! $option->isEmpty()) {
* $result += $option->get();
* }
* ```
*
* @template S
*
* @param S $initialValue
* @param callable(S, T):S $callable
*
* @return S
*/
abstract public function foldLeft($initialValue, $callable);
/**
* foldLeft() but with reversed arguments for the callable.
*
* @template S
*
* @param S $initialValue
* @param callable(T, S):S $callable
*
* @return S
*/
abstract public function foldRight($initialValue, $callable);
}