SIMPLE USAGE

    package Direction;
    
    use Class::Constant NORTH, EAST, SOUTH, WEST;

This generates four constants which can be assigned to some variable:

    my $facing = Direction::NORTH;

There are two major differences between Class::Constant constants and constants created by the constant pragma:

• Class::Constant constants have no inherent value, and as such only compare equal to themselves (but see "ORDINAL VALUES", eg:

      if ($facing == Direction::EAST) {
          print "you are facing east\n";
      }
      

• Class::Constant constants are actually objects blessed into the package that created them, so they have a "type", of sorts:

      if ($facing->isa("Direction")) {
          ...
      }
      

Neither of these distinctions are particularly useful in this simple usage, but are useful when using the more advanced features of this module, described below.

CONSTANT VALUES

Stringification

Constants can be declared with a string that will be returned when the constant is stringified (eg by "print"). For example:

    use Class::Constant
        NORTH => "north",
        EAST  => "east",
        SOUTH => "south",
        WEST  => "west";

This makes the following possible:

    print "you are facing $facing\n";

Named sub-constants

You can also declare other constant values that are associated with a constant:

    use Class::Constant
        NORTH => { x =>  0, y => -1 },
        EAST  => { x => -1, y =>  0 },
        SOUTH => { x =>  0, y =>  1 },
        WEST  => { x =>  1, y =>  0 };

These sub-constants are accessed via "get_*" methods called on the constant object:

    move_player($facing->get_x, $facing->get_y);

Combining the two

Of course both a string value and named sub-constants can be declared at the same time:

    use Class::Constant
        NORTH => "north",
                 { x =>  0, y => -1 },
        EAST  => "east",
                 { x => -1, y =>  0 },
        SOUTH => "south",
                 { x =>  0, y =>  1 },
        WEST  => "west",
                 { x =>  1, y =>  0 };

ORDINAL VALUES

    NORTH   0
    EAST    2
    SOUTH   1
    WEST    3

The ordinal value for a constant can be retrieved by calling the "get_ordinal" method on a constant object:

    my $ordinal = Direction::EAST->get_ordinal;

You can also retrieve a constant by its ordinal value using the class method "by_ordinal"

    my $west = Direction->by_ordinal(3);

These two methods are typically used together to fetch the "next" or "previous" constant in the sequence, eg:

    sub turn_left {
        my ($facing) = @_;
        return Direction->by_ordinal(($facing->get_ordinal - 1) % 4);
    }

OVERLOADING

Class::Constant::Object has "as_string" and "equals" methods, and also sets up overloading for the "" (stringification) and "==" and "!=" (equality) operators to use these methods. If you override these methods in your package, then Class::Constant::Object will arrange to call your methods instead.