I ran into a case where I had to get the string representation of a constant based only on its value, so a little digging around and some experimentation produced this:
const MY_CONSTANT = 1;
// get constant name by value
$class = new ReflectionClass('MyClassName');
$constants = array_flip($class->getConstants());
// output is "MY_CONSTANT"
If you’re in an instance method and want to retrieve the constants of the current class, use
get_class($this) here for the ReflectionClass constructor argument.