How to Retrieve Class Constants in PHP?

Obtaining Constant Definitions from PHP Classes

In certain scenarios, it becomes necessary to retrieve a list of constants defined within PHP classes. This may be particularly useful when introspection is required for dynamic code generation or analysis. The get_defined_constants() function, unfortunately, does not provide information specific to individual classes.

Using Reflection for Constant Retrieval

To address this limitation, Reflection can be employed. The ReflectionClass object provides access to class metadata, including the defined constants.

class Profile {
    const LABEL_FIRST_NAME = "First Name";
    const LABEL_LAST_NAME = "Last Name";
    const LABEL_COMPANY_NAME = "Company";
}

$refl = new ReflectionClass('Profile');
$constants = $refl->getConstants();

The getConstants() method returns an array containing all the constants declared in the class.

Output:

Array
(
    'LABEL_FIRST_NAME' => 'First Name',
    'LABEL_LAST_NAME' => 'Last Name',
    'LABEL_COMPANY_NAME' => 'Company'
)

Customizing Output Format

If a specific output format is desired, the class metadata can be further processed.

Retrieving Constant Names:

$constantNames = array_keys($constants);

Output:

Array
(
    'LABEL_FIRST_NAME',
    'LABEL_LAST_NAME',
    'LABEL_COMPANY_NAME'
)

Retrieving Fully Qualified Constant Names:

$fullyQualifiedConstantNames = array();
foreach ($constants as $name => $value) {
    $fullyQualifiedConstantNames[] = 'Profile::' . $name;
}

Output:

Array
(
    'Profile::LABEL_FIRST_NAME',
    'Profile::LABEL_LAST_NAME',
    'Profile::LABEL_COMPANY_NAME'
)

Retrieving Constant Names and Values:

$constantNamesWithValues = array();
foreach ($constants as $name => $value) {
    $constantNamesWithValues['Profile::' . $name] = $value;
}

Output:

Array
(
    'Profile::LABEL_FIRST_NAME' => 'First Name',
    'Profile::LABEL_LAST_NAME' => 'Last Name',
    'Profile::LABEL_COMPANY_NAME' => 'Company'
)

By leveraging Reflection, programmers can conveniently obtain and manipulate information about constants defined within PHP classes, enabling a wide range of flexibility for code generation, analysis, and other operations.

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