> User.find(:all, :conditions=>['arr @> ?', [1,2,3].pg])
  SELECT * FROM "users" WHERE ('arr' @> E'{"1", "2", "3"}')
> User.find(:all, :conditions=>['arr @> ?', [1,2,3].pg(:integer)])
  SELECT * FROM "users" WHERE (arr @> '{1,2,3}')
> User.find(:all, :conditions=>['arr @> ?', [1,2,3].pg(:float)])
  SELECT * FROM "users" WHERE (arr @> '{1.0,2.0,3.0}')
> u = User.find(1)
  SELECT * FROM "users" WHERE ("users"."id" = 1)
  => #<User id: 1, ..., arr: [1,2]>
> u.arr = [3,4]
> u.save
  UPDATE "users" SET "db_ar" = '{3.0,4.0}' WHERE "id" = 19
> User.find(:all, :conditions=>{:arr=>[3,4].pg})
  SELECT * FROM "users" WHERE ("users"."arr" = E'{"3", "4"}')
> User.find(:all, :conditions=>{:arr=>[3,4].search_any(:float)})
  SELECT * FROM "users" WHERE ("users"."arr" && '{3.0,4.0}')
> User.find(:all, :conditions=>{:arr=>[3,4].search_all(:integer)})
  SELECT * FROM "users" WHERE ("users"."arr" @> '{3,4}')
> User.find(:all, :conditions=>{:arr=>[3,4].search_subarray(:safe)})
  SELECT * FROM "users" WHERE ("users"."arr" <@ '{3,4}')
  
  class U < ActiveRecord::Migration
    def self.up
      create_table :users do |t|
        t.integer_array :int_ar
      end
      add_column :users, :fl_ar, :float_array
    end
  end

gem install ar_pg_array

Since version 0.9.13 ar_pg_array will try to detect arrays changed inplace.
And parsed arrays are now cached in @attributes_cache.
Thanks to Romain Beauxis (https://github.com/toots ) for being insistent about this.