strange ruby behavior with a constant -

could explain me, why original constant list beginning getting manipulated @ end? thought constant once initialized. want store manipulations in new array (new_list) without affecting original 1 (list).

$ned = "foo" $med = ""  print list = [:nrd, :mrd_y] # -> [:nrd, :mrd_y]   list = list  new_list = list.delete_if { |element|   case element   when :nrd $ned.empty?   when :mrd_y $ned.empty? || $med.empty?   end }  print new_list # -> [:nrd]  print list # -> [:nrd] instead of [:nrd, :mrd_y] 

array#delete_if -> deletes every element of self block evaluates true.

$ned = "foo" $med = ""  list = [:nrd, :mrd_y] p list.object_id #=> 84053120 list = list p list.object_id #=> 84053120 new_list = list.delete_if { |element|   case element   when :nrd $ned.empty?   when :mrd_y $ned.empty? || $med.empty?   end } 

list , list holding same array object, object_id tells above. each true evaluation block delete_if deletes item object referenced 84053120. kept list , list. can use below:

$ned = "foo" $med = ""  list = [:nrd, :mrd_y]  list = list new_list = list.dup.delete_if { |element|   case element   when :nrd $ned.empty?   when :mrd_y $ned.empty? || $med.empty?   end }  p new_list #=>[:nrd] p list #=>[:nrd, :mrd_y] 

or (better approach use array#reject),

$ned = "foo" $med = ""  list = [:nrd, :mrd_y]   new_list = list.reject { |element|   case element   when :nrd $ned.empty?   when :mrd_y $ned.empty? || $med.empty?   end } p new_list #=>[:nrd] p list #=>[:nrd, :mrd_y]