Ruby Mapping for Enumerations
Ruby does not have an enumerated type, so a Slice enumeration is emulated using a Ruby class: the name of the Slice enumeration becomes the name of the Ruby class; for each enumerator, the class contains a constant with the same name as the enumerator. For example:
enum Fruit { Apple, Pear, Orange };
The generated Ruby class looks as follows:
class Fruit
include Comparable
Apple = # ...
Pear = # ...
Orange = # ...
def Fruit.from_int(val)
def to_i
def to_s
def <=>(other)
def hash
# ...
end
The compiler generates a class constant for each enumerator that holds a corresponding instance of Fruit. The from_int class method returns an instance given its Slice value, while to_i returns the Slice value of an enumerator and to_s returns its Slice identifier.
Given the above definitions, we can use enumerated values as follows:
f1 = Fruit::Apple
f2 = Fruit::Orange
if f1 == Fruit::Apple # Compare for equality
# ...
if f1 < f2 # Compare two enums
# ...
case f2
when Fruit::Orange
puts "found Orange"
else
puts "found #{f2.to_s}"
end
Comparison operators are available as a result of including Comparable, which means a program can compare enumerators according to their Slice values. Note that, when using custom enumerator values, the order of enumerators by their Slice values may not match their order of declaration.
Suppose we modify the Slice definition to include a custom enumerator value:
enum Fruit { Apple, Pear = 3, Orange };
We can use from_int to examine the Slice values of the enumerators:
Fruit::from_int(0) # Apple Fruit::from_int(1) # nil Fruit::from_int(3) # Pear Fruit::from_int(4) # Orange