Ruby variables are invalid in the development mode.

Class variables are used in paging. They are mainly used to mark the ID of the "page number input box ".

If a page has several pages, the ID of the "page number input box" must be different to identify which page is to be paged. The class variable is used to achieve this purpose, so that all object instances share a variable without the need to re-initialize the variable each time.

Sample Code for using class variables

   1  require 'ruby-debug'     2  debugger   3  class Myclassvar   4    @@a=1   5    puts 1111111111111111111111   6    puts @@a   7     8    def testa   9      @@a=@@a+5   10    end    11    def testb   12      @@a=@@a+3   13      end   14    end   15       16    class Reclassvar < Myclassvar   17      def testa   18         @@a+=10   19      end   20    end    21       22     obj=Myclassvar.new   23     puts obj.testa   24     puts obj.testb   25     obj2=Myclassvar.new   26     puts obj2.testb   27     obj3=Reclassvar.new   28     puts obj3.testa

The execution sequence is 3 => 4 => 5 => 6 => 8 => 11 => 16 => 17 => 22 => 23 => 9 => 24 => 12 => 25 => 26 => 12 ......

The local Test variables fully conform to the expectation, but the class variables used in the project paging are initialized every time, once depressing. The result is that config. cache_classes = false is included in the configuration of rails in the Development Mode. Therefore, you can view the running result of the updated code every time you do not need to restart the service. The program on the server is enabled in the production mode, where config. cache_classes = true. This is why the class variable fails in the Development Mode. Every time a class is reloaded, all its class variables will be reinitialized.