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

When building tools that inspect PHP code, ReflectionClassConstant::isDeprecated() helps answer a focused question: checks whether the class constant carries the Deprecation attribute in PHP versions that support it.

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

What Is ReflectionClassConstant::isDeprecated()?

Checks whether the class constant carries the Deprecation attribute in PHP versions that support it.

Its method signature is:

public function isDeprecated(): 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, "KIND");

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

Output:

bool(false)

Explanation: Checks whether the class constant carries the Deprecation attribute in PHP versions that support it.

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, "RETENTION_DAYS");

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

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

Output:

bool(false)

Result type: bool

Explanation: A comment saying deprecated is not equivalent to the built-in deprecation marker.

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, "INTERNAL");

$result = $constantReflection->isDeprecated();
var_dump($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: getAttributes lists the constant's reflection attributes.

Important Behavior and Edge Cases

• A comment saying deprecated is not equivalent to the built-in deprecation marker.
• getAttributes lists the constant's reflection attributes.
• 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 class constant carries the Deprecation attribute in PHP versions that support it.
• A comment saying deprecated is not equivalent to the built-in deprecation marker.
• getAttributes lists the constant's reflection attributes.

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