pod install for different swift version

Podfile

  post_install do |installer|
      #setting all pods to 4.1
      installer.pods_project.targets.each do |target|
          target.build_configurations.each do |config|
              config.build_settings['SWIFT_VERSION'] = '4.1'
          end
      end
      
      #some libs uses the old version 4 only.
      installer.pods_project.targets.each do |target|
          if ['Alamofire', 'AlamofireImage', 'DropDown', 'IQKeyboardManagerSwift', 'KeychainSwift',  'SideMenu'].include? target.name
              target.build_configurations.each do |config|
                  config.build_settings['SWIFT_VERSION'] = '4'
              end
          end
      end
      
      #some pods have already made the transition, they'd work on 4.2
      installer.pods_project.targets.each do |target|
          if ['SwiftMessages', 'AlamofireNetworkActivityIndicator'].include? target.name
              target.build_configurations.each do |config|
                  config.build_settings['SWIFT_VERSION'] = '4.2'
              end
          end
      end
  end