A Podfile that demonstrates how to use dependencies that use an older Swift version

Podfile

target 'MyTarget' do
    use_frameworks!

    # Post installation script that enables the Swift 4.2 compiler's
    # legacy 4.1 mode for 4.2-incompatible pods
    post_install do |installer|
      incompatiblePods = ['PodA', 'PodB']

      installer.pods_project.targets.each do |target|
          if incompatiblePods.include? target.name
              target.build_configurations.each do |config|
                  # Replace with whichever Swift version you're migrating from
                  config.build_settings['SWIFT_VERSION'] = '4.1'
              end
          end
      end
    end

    pod 'Unbox'
    pod 'Wrap'
end