Add Result and tests
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src/Result.php
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168
src/Result.php
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<?php
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/**
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* @author Daniel J. Summers <daniel@bitbadger.solutions>
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* @license MIT
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*/
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declare(strict_types=1);
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namespace BitBadger\InspiredByFSharp;
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use InvalidArgumentException;
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/**
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* The result of an operation; one of two possible outcomes.
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*
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* While exceptions are still possible in F# (and PHP), a more robust model is returning an object that can represent
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* either success or failure. The `Result` type exposes an `OK` state for the successful result of an action and an
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* `Error` state for the unsuccessful result of that action. Neither result value can be `null`; both should be
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* meaningful for the action, and either eventuality should be handled by calling code.
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*
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* The net result _(no pun intended)_ is code that fails gracefully, and calling code that is aware that not every call
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* is successful.
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*
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* @template TOK The type of the OK result
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* @template TError The type of the error result
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*/
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readonly class Result
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{
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/** @var Option<TOK> The OK value for this result */
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private Option $okValue;
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/** @var Option<TError> The error value for this result */
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private Option $errorValue;
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/**
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* Constructor
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*
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* @param TOK|null $okValue The OK value for this result
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* @param TError|null $errorValue The error value for this result
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*/
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private function __construct(mixed $okValue = null, mixed $errorValue = null)
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{
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$this->okValue = Option::of($okValue);
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$this->errorValue = Option::of($errorValue);
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}
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/**
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* Get the value for an `OK` result
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*
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* @return TOK The OK value for this result
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* @throws InvalidArgumentException If the result is an `Error` result
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*/
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public function getOK(): mixed
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{
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return $this->okValue->get();
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}
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/**
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* Get the value for an `Error` result
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*
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* @return TError The error value for this result
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* @throws InvalidArgumentException If the result is an `OK` result
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*/
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public function getError(): mixed
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{
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return $this->errorValue->get();
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}
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/**
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* Create an `OK` result
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*
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* @param TOK $value The OK value for this result
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* @return Result<TOK, TError> The `OK` result for the value specified
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*/
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public static function OK(mixed $value): self
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{
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if (is_null($value)) {
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throw new InvalidArgumentException('Cannot use null as an OK value');
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}
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return new self(okValue: $value);
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}
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/**
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* Create an `Error` result
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*
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* @param TError $value The error value for this result
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* @return Result<TOK, TError> The `Error` result for the value specified
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*/
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public static function Error(mixed $value): self
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{
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if (is_null($value)) {
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throw new InvalidArgumentException('Cannot use null as an Error value');
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}
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return new self(errorValue: $value);
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}
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/**
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* Is the given result `OK`?
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*
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* @param Result $it The result in question
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* @return bool True if the result is `OK`, false if it is `Error`
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*/
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public static function isOK(Result $it): bool
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{
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return Option::isSome($it->okValue);
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}
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/**
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* Is the given result `Error`?
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*
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* @param Result $it The result in question
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* @return bool True if the result is `Error`, false if it is `OK`
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*/
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public static function isError(Result $it): bool
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{
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return Option::isSome($it->errorValue);
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}
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/**
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* Map an `OK` result to another, leaving an `Error` result unmodified
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*
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* @template U The type of the mapping function
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* @param callable(TOK): U $f The mapping function
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* @param Result<TOK, TError> $it The result in question
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* @return Result<U, TError> A transformed `OK` instance, or an `Error` instance with the same value
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*/
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public static function map(callable $f, Result $it): self
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{
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return self::isOK($it) ? self::OK($f($it->getOK())) : self::Error($it->getError());
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}
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/**
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* Map an `Error` result to another, leaving an `OK` result unmodified
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*
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* @template U The type of the mapping function
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* @param callable(TError): U $f The mapping function
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* @param Result<TOK, TError> $it The result in question
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* @return Result<TOK, U> A transformed `Error` instance, or an `OK` instance with the same value
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*/
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public static function mapError(callable $f, Result $it): self
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{
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return self::isError($it) ? self::Error($f($it->getError())) : self::OK($it->getOK());
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}
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/**
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* Execute a function on an `OK` value (if it exists)
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*
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* @param callable(TOK): void $f The function to call
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* @param Result<TOK, TError> $it The result in question
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*/
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public static function iter(callable $f, Result $it): void
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{
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if (self::isOK($it)) {
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$f($it->getOK());
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}
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}
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/**
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* Transform a `Result`'s `OK` value to an `Option`
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*
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* @param Result<TOK, TError> $it The result in question
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* @return Option<TOK> A `Some` option with the OK value if `OK`, `None` if `Error`
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*/
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public static function toOption(Result $it): Option
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{
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return Result::isOK($it) ? Option::Some($it->getOK()) : Option::None();
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}
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}
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200
tests/ResultTest.php
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200
tests/ResultTest.php
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<?php
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/**
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* @author Daniel J. Summers <daniel@bitbadger.solutions>
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* @license MIT
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*/
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declare(strict_types=1);
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namespace Test;
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use BitBadger\InspiredByFSharp\Option;
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use BitBadger\InspiredByFSharp\Result;
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use InvalidArgumentException;
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use PHPUnit\Framework\Attributes\TestDox;
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use PHPUnit\Framework\TestCase;
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/**
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* Unit tests for the Result class
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*/
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class ResultTest extends TestCase
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{
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#[TestDox('GetOK succeeds for OK result')]
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public function testGetOKSucceedsForOKResult(): void
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{
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$result = Result::OK('yay');
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$this->assertEquals('yay', $result->getOK(), 'The OK result should have been returned');
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}
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#[TestDox('GetOK fails for Error result')]
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public function testGetOKFailsForErrorResult(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::Error('whoops')->getOK();
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}
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#[TestDox('GetError succeeds for Error result')]
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public function testGetErrorSucceedsForErrorResult(): void
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{
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$result = Result::Error('boo');
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$this->assertEquals('boo', $result->getError(), 'The Error result should have been returned');
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}
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#[TestDox('GetError fails for OK result')]
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public function testGetErrorFailsForOKResult(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::OK('yeah')->getError();
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}
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#[TestDox('OK succeeds for non null result')]
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public function testOKSucceedsForNonNullResult(): void
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{
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$result = Result::OK('something');
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$this->assertTrue(Result::isOK($result), 'The result should have been "OK"');
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$this->assertEquals('something', $result->getOK(), 'The "OK" value was incorrect');
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}
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#[TestDox('OK fails for null result')]
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public function testOKFailsForNullResult(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::OK(null);
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}
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#[TestDox('Error succeeds for non null result')]
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public function testErrorSucceedsForNonNullResult(): void
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{
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$result = Result::Error('sad trombone');
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$this->assertTrue(Result::isError($result), 'The result should have been "Error"');
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$this->assertEquals('sad trombone', $result->getError(), 'The "Error" value was incorrect');
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}
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#[TestDox('Error fails for null result')]
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public function testErrorFailsForNullResult(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::Error(null);
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}
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#[TestDox('IsOK succeeds for OK result')]
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public function testIsOKSucceedsForOKResult(): void
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{
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$result = Result::OK('ok');
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$this->assertTrue(Result::isOK($result), 'The check for "OK" should have returned true');
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}
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#[TestDox('IsOK succeeds for Error result')]
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public function testIsOKSucceedsForErrorResult(): void
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{
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$result = Result::Error('error');
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$this->assertFalse(Result::isOK($result), 'The check for "OK" should have returned false');
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}
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#[TestDox('IsError succeeds for Error result')]
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public function testIsErrorSucceedsForErrorResult(): void
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{
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$result = Result::Error('not ok');
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$this->assertTrue(Result::isError($result), 'The check for "Error" should have returned true');
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}
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#[TestDox('IsError succeeds for OK result')]
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public function testIsErrorSucceedsForOKResult(): void
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{
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$result = Result::OK('fine');
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$this->assertFalse(Result::isError($result), 'The check for "Error" should have returned false');
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}
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#[TestDox('Map succeeds for OK result')]
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public function testMapSucceedsForOKResult(): void
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{
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$ok = Result::OK('yard');
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$mapped = Result::map(fn($it) => strrev($it), $ok);
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$this->assertTrue(Result::isOK($mapped), 'The mapped result should be "OK"');
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$this->assertEquals('dray', $mapped->getOK(), 'The mapping function was not called correctly');
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}
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#[TestDox('Map fails for OK result when mapping is null')]
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public function testMapFailsForOKResultWhenMappingIsNull(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::map(fn($it) => null, Result::OK('not null'));
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}
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#[TestDox('Map succeeds for Error result')]
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public function testMapSucceedsForErrorResult(): void
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{
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$tattle = new class { public bool $called = false; };
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$error = Result::Error('nope');
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$mapped = Result::map(function ($ignored) use ($tattle)
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{
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$tattle->called = true;
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return 'hello';
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}, $error);
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$this->assertTrue(Result::isError($mapped), 'The mapped result should be "Error"');
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$this->assertFalse($tattle->called, 'The mapping function should not have been called');
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$this->assertNotSame($error, $mapped, 'There should have been a new "Error" instance returned');
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}
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#[TestDox('MapError succeeds for OK result')]
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public function testMapErrorSucceedsForOKResult(): void
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{
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$tattle = new class { public bool $called = false; };
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$ok = Result::OK('sure');
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$mapped = Result::mapError(function ($ignored) use ($tattle)
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{
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$tattle->called = true;
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return 'hello';
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}, $ok);
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$this->assertTrue(Result::isOK($mapped), 'The mapped result should be "OK"');
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$this->assertFalse($tattle->called, 'The mapping function should not have been called');
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$this->assertNotSame($ok, $mapped, 'There should have been a new "OK" instance returned');
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}
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#[TestDox('MapError succeeds for Error result')]
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public function testMapErrorSucceedsForErrorResult(): void
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{
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$error = Result::Error('taco');
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$mapped = Result::mapError(fn($it) => str_repeat('*', strlen($it)), $error);
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$this->assertTrue(Result::isError($mapped), 'The mapped result should be "Error"');
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$this->assertEquals('****', $mapped->getError(), 'The mapping function was not called correctly');
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}
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#[TestDox('MapError fails for Error result when mapping is null')]
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public function testMapErrorFailsForErrorResultWhenMappingIsNull(): void
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{
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$this->expectException(InvalidArgumentException::class);
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Result::mapError(fn($it) => null, Result::Error('pizza'));
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}
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#[TestDox('Iter succeeds for OK result')]
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public function testIterSucceedsForOKResult(): void
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{
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$target = new class { public mixed $called = null; };
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Result::iter(function ($it) use ($target) { $target->called = $it; }, Result::OK(77));
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$this->assertEquals(77, $target->called, 'The function should have been called with the "OK" value');
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}
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#[TestDox('Iter succeeds for Error result')]
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public function testIterSucceedsForErrorResult(): void
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{
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$target = new class { public mixed $called = null; };
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Result::iter(function ($ignored) use ($target) { $target->called = 'uh oh'; }, Result::Error(''));
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$this->assertNull($target->called, 'The function should not have been called');
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}
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#[TestDox('ToOption succeeds for OK result')]
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public function testToOptionSucceedsForOKResult()
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{
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$value = Result::toOption(Result::OK(99));
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$this->assertTrue(Option::isSome($value), 'An "OK" result should map to a "Some" option');
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$this->assertEquals(99, $value->get(), 'The value is not correct');
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}
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#[TestDox('ToOption succeeds for Error result')]
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public function testToOptionSucceedsForErrorResult()
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{
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$value = Result::toOption(Result::Error('file not found'));
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$this->assertTrue(Option::isNone($value), 'An "Error" result should map to a "None" option');
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}
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}
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