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AydinHassanAydinHassan
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Merge pull request #24 from php-school/static-return-type
Static return type
2 parents bcd0812 + 3f2012f commit 6da7523

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‎app/bootstrap.php‎

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use PhpSchool\PHP8Appreciate\Exercise\InfiniteDivisions;
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use PhpSchool\PHP8Appreciate\Exercise\PhpPromotion;
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use PhpSchool\PHP8Appreciate\Exercise\LordOfTheStrings;
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use PhpSchool\PHP8Appreciate\Exercise\TheReturnOfStatic;
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use PhpSchool\PHP8Appreciate\Exercise\UniteTheTypes;
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use PhpSchool\PhpWorkshop\Application;
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$app->addExercise(InfiniteDivisions::class);
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$app->addExercise(ASafeSpaceForNulls::class);
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$app->addExercise(AllMixedUp::class);
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$app->addExercise(TheReturnOfStatic::class);
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$art = <<<ART
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_ __ _

‎app/config.php‎

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use PhpSchool\PHP8Appreciate\Exercise\InfiniteDivisions;
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use PhpSchool\PHP8Appreciate\Exercise\PhpPromotion;
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use PhpSchool\PHP8Appreciate\Exercise\LordOfTheStrings;
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use PhpSchool\PHP8Appreciate\Exercise\TheReturnOfStatic;
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use PhpSchool\PHP8Appreciate\Exercise\UniteTheTypes;
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use Psr\Container\ContainerInterface;
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},
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AllMixedUp::class => function (ContainerInterface $c) {
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return new AllMixedUp($c->get(PhpParser\Parser::class), $c->get(\Faker\Generator::class));
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},
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TheReturnOfStatic::class => function (ContainerInterface $c) {
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return new TheReturnOfStatic($c->get(PhpParser\Parser::class));
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}
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];

‎exercises/the-return-of-static/initial/the-return-of-static.php‎

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<?php
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class File
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{
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private ?string $permissions = null;
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public function withPermissions(string $permissions): static
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{
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$clone = new self();
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$clone->permissions = $permissions;
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return $clone;
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}
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}
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class Image extends File
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{
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private ?string $ext = null;
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private ?string $crop = null;
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public function withExt(string $ext): static
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{
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$clone = clone $this;
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$clone->ext = $ext;
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return $clone;
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}
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public function withCrop(string $crop): static
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{
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$clone = clone $this;
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$clone->crop = $crop;
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return $clone;
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}
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}
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$image = (new Image())
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->withPermissions('w+')
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->withExt('jpeg')
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->withCrop('16x9');
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var_dump($image);

‎exercises/the-return-of-static/problem/problem.md‎

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You have been given a piece of code (look for `the-return-of-static.php` in your working directory) which is using static return types.
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You will find two classes. `File`, a base class, and `Image` a class extending and adding behavior to `File`. We instantiate `Image`, set some properties using a fluent interface and then dump the object using `var_dump`.
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If you run the code using `{appname} run the-return-of-static.php` you will see it is broken.
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Locate and fix the issue!
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### The advantages of the static return type
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* Enforces that an instance of the class the method is called from, is returned.
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* Most useful for fluent interfaces and static constructors to ensure an instance of a parent class is not returned.
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----------------------------------------------------------------------
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## HINTS
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(Brief) Documentation on the static return type feature can be found by pointing your browser here:
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[https://www.php.net/manual/en/language.types.declarations.php#language.types.declarations.static]()
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The static return type enforces methods to return an instance of the class that the method was called from, rather than the one it was defined in.
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‎exercises/the-return-of-static/solution/solution.php‎

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<?php
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class File
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{
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private ?string $permissions = null;
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public function withPermissions(string $permissions): static
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{
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$clone = clone $this;
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$clone->permissions = $permissions;
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return $clone;
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}
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}
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class Image extends File
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{
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private ?string $ext = null;
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private ?string $crop = null;
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public function withExt(string $ext): static
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{
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$clone = clone $this;
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$clone->ext = $ext;
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return $clone;
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}
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public function withCrop(string $crop): static
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{
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$clone = clone $this;
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$clone->crop = $crop;
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return $clone;
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}
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}
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$image = (new Image())
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->withPermissions('w+')
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->withExt('jpeg')
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->withCrop('16x9');
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var_dump($image);

‎src/Exercise/TheReturnOfStatic.php‎

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<?php
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namespace PhpSchool\PHP8Appreciate\Exercise;
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use PhpParser\Node;
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use PhpParser\Node\Expr\Assign;
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use PhpParser\Node\Expr\Clone_;
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use PhpParser\Node\Expr\Variable;
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use PhpParser\Node\Stmt;
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use PhpParser\Node\Stmt\ClassMethod;
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use PhpParser\Node\Stmt\Expression;
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use PhpParser\Node\Stmt\Function_;
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use PhpParser\NodeFinder;
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use PhpParser\Parser;
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use PhpSchool\PhpWorkshop\Exercise\AbstractExercise;
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use PhpSchool\PhpWorkshop\Exercise\CliExercise;
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use PhpSchool\PhpWorkshop\Exercise\ExerciseInterface;
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use PhpSchool\PhpWorkshop\Exercise\ExerciseType;
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use PhpSchool\PhpWorkshop\Exercise\ProvidesInitialCode;
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use PhpSchool\PhpWorkshop\ExerciseCheck\SelfCheck;
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use PhpSchool\PhpWorkshop\Input\Input;
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use PhpSchool\PhpWorkshop\Result\Failure;
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use PhpSchool\PhpWorkshop\Result\ResultInterface;
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use PhpSchool\PhpWorkshop\Result\Success;
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use PhpSchool\PhpWorkshop\Solution\SingleFileSolution;
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use PhpSchool\PhpWorkshop\Solution\SolutionInterface;
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class TheReturnOfStatic extends AbstractExercise implements
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ExerciseInterface,
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ProvidesInitialCode,
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CliExercise,
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SelfCheck
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{
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public function __construct(private Parser $parser)
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{
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}
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public function getName(): string
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{
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return 'The Return of Static';
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}
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public function getDescription(): string
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{
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return 'PHP 8\'s static return types';
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}
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public function getInitialCode(): SolutionInterface
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{
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return SingleFileSolution::fromFile(
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__DIR__ . '/../../exercises/the-return-of-static/initial/the-return-of-static.php'
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);
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}
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public function getType(): ExerciseType
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{
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return ExerciseType::CLI();
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}
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public function getArgs(): array
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{
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return [];
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}
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public function check(Input $input): ResultInterface
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{
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/** @var array<Stmt> $statements */
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$statements = $this->parser->parse((string) file_get_contents($input->getRequiredArgument('program')));
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$finder = new NodeFinder();
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/** @var Stmt\Class_|null $class */
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$class = $finder->findFirst($statements, function (Node $node) {
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return $node instanceof Stmt\Class_ && $node->name && $node->name->toString() === 'File';
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});
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/** @var ClassMethod|null $method */
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$method = $finder->findFirst($class ? [$class] : [], function (Node $node) {
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return $node instanceof ClassMethod && $node->name->toString() === 'withPermissions';
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});
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if (!$class || !$method) {
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return new Failure($this->getName(), 'The method withPermissions cannot be found');
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}
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if (!($assign = $this->findAssignOnFirstLine($method))) {
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return new Failure($this->getName(), 'The first statement in withPermissions is not an assign');
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}
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if ($this->isCloneOfThis($assign)) {
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return new Success($this->getName());
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}
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return new Failure($this->getName(), 'The first statement is not a clone of `$this`');
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}
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private function findAssignOnFirstLine(ClassMethod $method): ?Assign
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{
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if (!isset($method->stmts[0])) {
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return null;
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}
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if (!$method->stmts[0] instanceof Expression) {
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return null;
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}
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if (!$method->stmts[0]->expr instanceof Assign) {
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return null;
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}
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return $method->stmts[0]->expr;
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}
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private function isCloneOfThis(Assign $assign): bool
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{
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if (!$assign->expr instanceof Clone_) {
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return false;
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}
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if (!$assign->expr->expr instanceof Variable) {
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return false;
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}
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return $assign->expr->expr->name === 'this';
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}
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}

‎test/Exercise/TheReturnOfStaticTest.php‎

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<?php
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namespace PhpSchool\PHP8AppreciateTest\Exercise;
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use PhpSchool\PHP8Appreciate\Exercise\TheReturnOfStatic;
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use PhpSchool\PhpWorkshop\Application;
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use PhpSchool\PhpWorkshop\Result\Failure;
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use PhpSchool\PhpWorkshop\TestUtils\WorkshopExerciseTest;
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class TheReturnOfStaticTest extends WorkshopExerciseTest
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{
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public function getExerciseClass(): string
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{
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return TheReturnOfStatic::class;
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}
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public function getApplication(): Application
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{
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return require __DIR__ . '/../../app/bootstrap.php';
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}
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public function testFailureWhenNoClassNameFile(): void
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{
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$this->runExercise('no-file-class.php');
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$this->assertVerifyWasNotSuccessful();
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$this->assertResultsHasFailure(Failure::class, 'The method withPermissions cannot be found');
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}
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public function testFailureWhenNoWithPermissionsMethod(): void
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{
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$this->runExercise('no-with-permissions-method.php');
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$this->assertVerifyWasNotSuccessful();
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$this->assertResultsHasFailure(Failure::class, 'The method withPermissions cannot be found');
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}
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public function testFailureWhenFirstStatementIsNotAnAssign(): void
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{
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$this->runExercise('no-assign-statement.php');
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$this->assertVerifyWasNotSuccessful();
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$this->assertResultsHasFailure(Failure::class, 'The first statement in withPermissions is not an assign');
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}
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public function testFailureWhenAssignIsNotClone(): void
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{
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$this->runExercise('no-clone.php');
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$this->assertVerifyWasNotSuccessful();
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$this->assertResultsHasFailure(Failure::class, 'The first statement is not a clone of `$this`');
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}
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public function testFailureWhenAssignIsNotCloneOfThis(): void
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{
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$this->runExercise('no-clone-this.php');
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$this->assertVerifyWasNotSuccessful();
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$this->assertResultsHasFailure(Failure::class, 'The first statement is not a clone of `$this`');
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}
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public function testSuccessfulSolution(): void
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{
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$this->runExercise('solution-correct.php');
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$this->assertVerifyWasSuccessful();
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}
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}

‎test/solutions/the-return-of-static/no-assign-statement.php‎

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<?php
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class File
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{
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private ?string $permissions = null;
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public function withPermissions(string $permissions): static
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{
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new static;
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$clone = clone $this;
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$clone->permissions = $permissions;
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return $clone;
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}
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}
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class Image extends File
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{
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private ?string $ext = null;
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private ?string $crop = null;
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public function withExt(string $ext): static
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{
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$clone = clone $this;
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$clone->ext = $ext;
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return $clone;
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}
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public function withCrop(string $crop): static
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{
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$clone = clone $this;
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$clone->crop = $crop;
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return $clone;
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}
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}
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$image = (new Image())->withPermissions('w+')->withExt('jpeg')->withCrop('16x9');
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var_dump($image);

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