constant_reference.rb

##
# Note from Ruby Pocket Reference
#
# Since constants refer to objects, the contents of the object
# to which the constant refers may change without Ruby generating
# a warning. Thus, Ruby constants are called *mutable*, because,
# although the constant is only expected to refer to a single
# object throughout the program, what's contained in that object
# may vary.

FOO = 'a'
FOO = 'b'
puts "FOO is #{FOO}"

class Bar
  attr_accessor :name
end

bar = Bar.new
bar.name = 'a'

BAR = bar
puts "BAR's name is #{BAR.name}"

bar.name = 'b'
puts "BAR's name is #{BAR.name}"

##### OUTPUT

# constant_reference.rb:2: warning: already initialized constant FOO
# constant_reference.rb:1: warning: previous definition of FOO was here
# FOO is b
# BAR's name is a
# BAR's name is b