Deep Closure Comparator Laravel Package

Getting Started

Install via Composer:

composer require --dev eliashaeussler/deep-closure-comparator

Then register the comparator in your PHPUnit configuration (phpunit.xml):

<phpunit>
    <extensions>
        <extension class="EliasHaeussler\DeepClosureComparator\PHPUnit\ComparatorExtension"/>
    </extensions>
</phpunit>

First use case: comparing two closures for structural equality (same parameters, same body, same static bindings) in unit tests:

$this->assertEquals(
    fn ($x) => $x * 2,
    $someVariableThatShouldBeTheSameClosure,
);

Implementation Patterns

• Testing higher-order functions: Verify that functions like map, filter, or custom wrappers return expected closures:

  $expected = fn ($item) => $item->isActive();
  $actual = $this->service->createFilter();
  $this->assertEquals($expected, $actual);
  

• Integration with factories/providers: Assert that dependency injection or factory methods produce closures matching predefined ones—especially useful for fluent APIs or configuration-based callback generation.
• Combine with Closure::fromCallable(): Validate when converting callables to closures:

  $callable = [$this, 'handler'];
  $closure = Closure::fromCallable($callable);
  $this->assertEquals(Closure::fromCallable([$this, 'handler']), $closure);
  

Gotchas and Tips

• Strict equality only: This comparator checks semantic equality—not reference identity. Two distinct closures with identical signature and body are considered equal.
• Static binding matters: Closures bound to different objects (e.g., via bindTo()) are not equal, even with identical code:

  $a = fn () => 42;
  $b = $a->bindTo(new StdClass());
  $this->assertNotEquals($a, $b); // ✅ Correctly different
  

• Reflection-dependent: Uses ReflectionFunction internally—avoid closures that rely on runtime-mutated state or anonymous classes referencing non-serializable resources.
• No support for internal closures: Closures wrapping internal (engine/ext) functions (e.g., strlen::class) cannot be compared meaningfully—expect EqualsComparisonException.
• PHP 8.0+ required: Uses typed properties and named arguments extensively; won’t work with PHP 7.x.