PHP ReflectionClassConstant::isPrivate() Method: Usage and Examples

When building tools that inspect PHP code, ReflectionClassConstant::isPrivate() helps answer a focused question: checks whether the reflected constant is private to its declaring class.

Reflection is useful in framework tooling, dependency injection, testing, code inspection and debugging.

What Is ReflectionClassConstant::isPrivate()?

Checks whether the reflected constant is private to its declaring class.

Its method signature is:

public function isPrivate(): bool

This method has no required arguments.

Return value: bool

Example 1: Inspect a typed constant

Start with a self-contained PHP declaration and inspect the method result.

<?php

declare(strict_types=1);

#[Attribute(Attribute::TARGET_CLASS_CONSTANT)]
class ConstantLabel { public function __construct(public string $value) {} }
class ReportLabels {
    /** Human-readable identifier for exported reports. */
    #[ConstantLabel('export')]
    final public const string KIND = 'csv';
    protected const int RETENTION_DAYS = 30;
    private const bool INTERNAL = true;
}
enum DeliveryStage: string { case Queued = 'queued'; case Sent = 'sent'; }

$constantReflection = new ReflectionClassConstant(ReportLabels::class, "INTERNAL");

$result = $constantReflection->isPrivate();
var_dump($result);

Output:

bool(true)

Explanation: Checks whether the reflected constant is private to its declaring class.

Example 2: Compare a constant with different visibility

Next, change the reflected declaration or parameter to observe a related situation.

<?php

declare(strict_types=1);

#[Attribute(Attribute::TARGET_CLASS_CONSTANT)]
class ConstantLabel { public function __construct(public string $value) {} }
class ReportLabels {
    /** Human-readable identifier for exported reports. */
    #[ConstantLabel('export')]
    final public const string KIND = 'csv';
    protected const int RETENTION_DAYS = 30;
    private const bool INTERNAL = true;
}
enum DeliveryStage: string { case Queued = 'queued'; case Sent = 'sent'; }

$constantReflection = new ReflectionClassConstant(ReportLabels::class, "KIND");

$result = $constantReflection->isPrivate();
var_dump($result);

// Check the returned value type before using the result.
echo "\nResult type: " . get_debug_type($result);

Output:

bool(false)

Result type: bool

Explanation: Private visibility differs from protected visibility in inheritance.

Practical Example: Inspect another declared constant

This final case shows how the same API can be used when inspecting application definitions.

<?php

declare(strict_types=1);

#[Attribute(Attribute::TARGET_CLASS_CONSTANT)]
class ConstantLabel { public function __construct(public string $value) {} }
class ReportLabels {
    /** Human-readable identifier for exported reports. */
    #[ConstantLabel('export')]
    final public const string KIND = 'csv';
    protected const int RETENTION_DAYS = 30;
    private const bool INTERNAL = true;
}
enum DeliveryStage: string { case Queued = 'queued'; case Sent = 'sent'; }

$constantReflection = new ReflectionClassConstant(ReportLabels::class, "RETENTION_DAYS");

$result = $constantReflection->isPrivate();
var_dump($result);

// Use the reflection result in a simple decision.
if (is_bool($result)) {
    echo "\nStatus: " . ($result ? "yes" : "no");
} elseif (is_array($result)) {
    echo "\nEntries: " . count($result);
} elseif ($result === null) {
    echo "\nNo value returned";
} else {
    echo "\nReflection result available";
}

Output:

bool(false)

Status: no

Explanation: isProtected and isPublic check other visibility levels.

Important Behavior and Edge Cases

• Private visibility differs from protected visibility in inheritance.
• isProtected and isPublic check other visibility levels.
• Reflection describes declarations and runtime state; requesting metadata does not automatically validate or sanitize application input.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Checks whether the reflected constant is private to its declaring class.
• Private visibility differs from protected visibility in inheritance.
• isProtected and isPublic check other visibility levels.

Use ReflectionClassConstant::isPrivate() when you need the precise metadata or behavior demonstrated above. Keep the target declaration and relevant PHP version in mind when adapting the examples.