feat: introduce method to get parameter by index

src/Definition/Exception/InvalidParameterIndex.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CuyZ\Valinor\Definition\Exception;
+
+use CuyZ\Valinor\Definition\Parameters;
+use LogicException;
+
+/** @internal */
+final class InvalidParameterIndex extends LogicException
+{
+    public function __construct(int $index, Parameters $parameters)
+    {
+        $max = $parameters->count() - 1;
+
+        parent::__construct(
+            "Index $index is out of range, it should be between 0 and $max.",
+            1644936619
+        );
+    }
+}

src/Definition/Parameters.php

@@ -5,10 +5,13 @@ declare(strict_types=1);
 namespace CuyZ\Valinor\Definition;
 
 use Countable;
+use CuyZ\Valinor\Definition\Exception\InvalidParameterIndex;
 use CuyZ\Valinor\Definition\Exception\ParameterNotFound;
 use IteratorAggregate;
 use Traversable;
 
+use function array_values;
+
 /**
  * @api
  *
@@ -40,6 +43,18 @@ final class Parameters implements IteratorAggregate, Countable
         return $this->parameters[$name];
     }
 
+    /**
+     * @param int<0, max> $index
+     */
+    public function at(int $index): ParameterDefinition
+    {
+        if ($index >= $this->count()) {
+            throw new InvalidParameterIndex($index, $this);
+        }
+
+        return array_values($this->parameters)[$index];
+    }
+
     public function count(): int
     {
         return count($this->parameters);

tests/Unit/Definition/ParametersTest.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace CuyZ\Valinor\Tests\Unit\Definition;
 
+use CuyZ\Valinor\Definition\Exception\InvalidParameterIndex;
 use CuyZ\Valinor\Definition\Exception\ParameterNotFound;
 use CuyZ\Valinor\Definition\Parameters;
 use CuyZ\Valinor\Tests\Fake\Definition\FakeParameterDefinition;
@@ -36,6 +37,25 @@ final class ParametersTest extends TestCase
         (new Parameters())->get('unknownParameter');
     }
 
+    public function test_get_parameter_at_index_returns_correct_parameter(): void
+    {
+        $parameterA = FakeParameterDefinition::new('SomeParameterA');
+        $parameterB = FakeParameterDefinition::new('SomeParameterB');
+        $parameters = new Parameters($parameterA, $parameterB);
+
+        self::assertSame($parameterA, $parameters->at(0));
+        self::assertSame($parameterB, $parameters->at(1));
+    }
+
+    public function test_get_parameter_at_index_out_of_range_throws_exception(): void
+    {
+        $this->expectException(InvalidParameterIndex::class);
+        $this->expectExceptionCode(1644936619);
+        $this->expectExceptionMessage('Index 1 is out of range, it should be between 0 and 0.');
+
+        (new Parameters(FakeParameterDefinition::new()))->at(1);
+    }
+
     public function test_parameters_are_countable(): void
     {
         $parameters = new Parameters(