RGB_COLORS = [:red, :green, :blue] # => [:red, :green, :blue]
RGB_COLORS << :purple # => [:red, :green, :blue, :purple]
RGB_COLORS = [:red, :green, :blue]
# warning: already initialized constant RGB_GOLORS
RGB_COLORS # => [:red, :green, :blue]
RGB_COLORS.freeze
RGB_COLORS << :purple
# TypeError: can't modify frozen array