Using Metaprogramming Instead of Ifs or Case Statements in Automation

At one time or another, an automation engineer has written the following ruby code below to select a menu option above.

def select_menu(choice)
  if choice == 'Users'    within(:xpath, ".//*[@'navbar-inner']//*[@'nav'])"
      click_on('Users')
    end
  elsif choice == 'Apps'
    within(:xpath, ".//*[@'navbar-inner']//*[@'nav'])"
      click_on(''Apps')
    end
  elsif choice == 'Activity'
    within(:xpath, ".//*[@'navbar-inner']//*[@'nav'])"
      click_on('Activity')
    end
  elsif choice == 'Settings'
    within(:xpath, ".//*[@'navbar-inner']//*[@'nav'])"
      click_on('Settings)
    end
  else
    $log.debug("Invalid Choice")
    exit 1
  end
end
 

Although this code works, maintenance can soon become a time consuming effort.  

1. If another menu option is added, another elsif will need to be added along with the within method
2. If the xpath of the menu bar where to change, then all the if/elsif statements would need to be update.

Thanks to metaprogramming, a more elegant and maintainable solution can now be written:

  ["Users", "Apps", "Activity", "Settings"].each do |menu|
    define_method("select_#{menu}") do
      within(:xpath, ".//*[@'navbar-inner']//*[@'nav']) do
        click_link("#{menu}")
      end
    end
  end

Metaprogramming is the act of writing code that operates on code rather than on data.  The define_method allows one to create methods programmatically using a method.  The 'def' method is not needed in this case.

In the newly rewritten code, ruby will now create 4 methods:

• select_Users
• select_Apps
• select_Activity
• select_Settings

This addresses the two maintenance issues pointed out earlier.  

1. Adding or removing a menu option is as simple as adding/removing an element in the given array, ["Users", "Apps", Activity", "Settings"]
2. Updating the location of the menu bar to query within is limited to one line

Additionally, if a menu is not defined, then there would not be an existing method.  This eliminates the need to have the else statement to handle the case of entering a menu option that does not exist.

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