Dynamic constant name in PHP

To use dynamic constant names in your class you can use reflection feature (since php5):

$thisClass = new ReflectionClass(__CLASS__);
$thisClass->getConstant($constName);

For example: if you want to filter only specific (SORT_*) constants in the class

class MyClass 
{
    const SORT_RELEVANCE = 1;
    const SORT_STARTDATE = 2;

    const DISTANCE_DEFAULT = 20;

    public static function getAvailableSortDirections()
    {
        $thisClass = new ReflectionClass(__CLASS__);
        $classConstants = array_keys($thisClass->getConstants());

        $sortDirections = [];
        foreach ($classConstants as $constName) {
            if (0 === strpos($constName, 'SORT_')) {
                $sortDirections[] =  $thisClass->getConstant($constName);
            }
        }

        return $sortDirections;
    }
}

var_dump(MyClass::getAvailableSortDirections());

result:

array (size=2)
  0 => int 1
  1 => int 2

http://dk.php.net/manual/en/function.constant.php

echo constant($constant_name);

And to demonstrate that this works with class constants too:

class Joshua {
    const SAY_HELLO = "Hello, World";
}

$command = "HELLO";
echo constant("Joshua::SAY_$command");