A Podfile that demonstrates how to use Swift 3 dependencies in a Swift 4 project

Podfile

target 'MyTarget' do
    use_frameworks!

    # Post installation script that enables the Swift 4 compiler's
    # legacy 3.2 mode for Swift 4-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|
                  config.build_settings['SWIFT_VERSION'] = '3.2'
              end
          end
      end
    end

    pod 'Unbox'
    pod 'Wrap'
end