ReflectionClass inspects the definition of a class, rather than running its constructor or calling its methods.
What Is ReflectionClass::getConstants in PHP?
Returns a name-to-value array of class constants visible through reflection.
ReflectionClass::getConstants(?int $filter = ...)Parameters:
$filter— Optional. An optional bitmask of ReflectionMethod or ReflectionProperty modifiers, depending on the method.
Example 1: Understanding the Basic Behavior
<?php
class Report { public const VERSION = 2; public string $title = 'Draft'; protected int $pages = 10; public static string $category = 'docs'; public function publish(): void {} }
$reflectionClass = new ReflectionClass(Report::class);
$result = $reflectionClass->getConstants();
var_dump($result);Output:
array(1) {
["VERSION"]=>
int(2)
}Explanation: Returns a name-to-value array of class constants visible through reflection.
Example 2: Testing Another Case
<?php
interface Exportable { public function export(): string; }
trait HasId { public function getId(): int { return 12; } }
class Invoice implements Exportable { use HasId; public string $name = 'Invoice'; public const STATE = 'open'; public function export(): string { return 'invoice'; } }
$reflectionClass = new ReflectionClass(Invoice::class);
$result = $reflectionClass->getConstants();
var_dump($result);Output:
array(1) {
["STATE"]=>
string(4) "open"
}Explanation: This method returns names mapped directly to constant values; descriptors require getReflectionConstants().
Practical Example: Applying the Operation
<?php
abstract class BaseJob { protected string $name = 'job'; abstract public function run(): void; }
class CompletedJob extends BaseJob { public function run(): void {} }
$reflectionClass = new ReflectionClass(CompletedJob::class);
$result = $reflectionClass->getConstants();
var_dump($result);Output:
array(0) {
}Explanation: The returned metadata may be false, null, an array, or a Reflection object depending on the requested property.
Important Behavior and Edge Cases
- This method returns names mapped directly to constant values; descriptors require getReflectionConstants().
- The returned metadata may be false, null, an array, or a Reflection object depending on the requested property.
Comparison With Related Approaches
| Approach | When to Use It |
|---|---|
ReflectionClass::getConstants | Returns a name-to-value array of class constants visible through reflection. |
ReflectionClass::getReflectionConstants() | getConstants() returns name/value pairs; getReflectionConstants() returns descriptor objects. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Treating metadata returned by ReflectionClass::getConstants() as though it executes the reflected class member. | This method returns names mapped directly to constant values; descriptors require getReflectionConstants(). |
| Choosing ReflectionClass::getReflectionConstants() without checking whether it provides the same result. | getConstants() returns name/value pairs; getReflectionConstants() returns descriptor objects. |
Key Takeaways
- Returns a name-to-value array of class constants visible through reflection.
- This method returns names mapped directly to constant values; descriptors require getReflectionConstants().
- The returned metadata may be false, null, an array, or a Reflection object depending on the requested property.
The examples demonstrate where ReflectionClass::getConstants fits within reflection and metadata. Verify the relevant preconditions whenever you adapt the code to real data.