redefining a class that sets a class variable will recreate the class variable

cvar.rb

class A
  @@cvar = {}

  def mutate
    @@cvar[:foo] = "bar"
  end

  def add(k,v)
    @@cvar[k] = v
  end

  def show
    p @@cvar
  end
end

a = A.new
a.mutate
p "before:"
a.show
a.add("yellow","elephant")

a.show

class A
  @@cvar = {}

  def mutate
    @@cvar[:baz] = "qux"
  end

  def show
    p @@cvar
  end
end

a = A.new
a.mutate
p "after:"
a.show

gistfile1.txt

"before:"
{:foo=>"bar"}
{:foo=>"bar", "yellow"=>"elephant"}
"after:"
{:baz=>"qux"}