目前最新swift是4.1，但是pod导入的三方可能是3.3版本，此时使用pod导入三方可在podfile里配置以下内容

# Swift 版本声明
post_install do |installer|
    installer.pods_project.targets.each do |target|
        if ['对应三方1', '对应三方2'].include? target.name
            target.build_configurations.each do |config|
                config.build_settings['SWIFT_VERSION'] = '3.3'
                config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
            end
            else
            target.build_configurations.each do |config|
                config.build_settings['SWIFT_VERSION'] = '4.1'
                config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
            end
        end
    end
end

整个podfile为

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '9.0'
use_frameworks!
inhibit_all_warnings!

target 'FoxBuy' do
  ## 此处是三方库
  ## ...
end

# Swift 版本声明
post_install do |installer|
    installer.pods_project.targets.each do |target|
        if ['对应三方1', '对应三方2'].include? target.name
            target.build_configurations.each do |config|
                config.build_settings['SWIFT_VERSION'] = '3.3'
                config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
            end
            else
            target.build_configurations.each do |config|
                config.build_settings['SWIFT_VERSION'] = '4.1'
                config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
            end
        end
    end
end