Cocoapods 编译条件数组处理

为什么非要定义一个变量，直接使用config.build_settings['SWIFT_ACTIVE_COMPILATION_CONDITIONS'] += ，说是个String，
直接拼接到 string 上了，很奇怪！

post_install do |installer|
  installer.pods_project.targets.each do |target|
    target.build_configurations.each do |config|

      conditions = ['$(inherited)']

      if config.name.include?("Test")
        conditions += ['TEST']
      end
      
      if config.name.include?("Debug") && config.name != 'Debug'
        conditions += ['DEBUG']
      end

      if target == 'WidgetExtension'
        conditions += ['WIDGET']
      end
      
      config.build_settings['SWIFT_ACTIVE_COMPILATION_CONDITIONS'] = conditions
      
    end
  end
end