title: swift dependency in objc podspec project
body: <p>I'm creating my first CocoaPod project (ObjC) which requires a Swift dependency. When I try to lint the project I get the error:</p>
  
  <blockquote>
    <p>Pods written in Swift can only be integrated as frameworks; add <code>use_frameworks!</code> to your Podfile or target to opt into using it.</p>
  </blockquote>
  
  <p>I understand how to do this when including a CocoaPod in a regular xcode project, but how do I solve this issue when the project is a CocoaPod? I tried adding the 'use_frameworks!' declaration in the podspec file but that doesn't seem to be correct.</p>
  
  <p>Here is my podspec file:</p>
  
  <pre><code>Pod::Spec.new do |s|
  
    s.name             = "my-custom-pod"
    s.version          = "0.0.1"
    s.summary          = "totally awesome stuff"
  
    s.description      = &lt;&lt;-DESC
                           more details about the totally awesome stuff, if only it worked :(
                         DESC
  
    s.homepage         = "https://awesomestuff.com"
    # s.screenshots     = "www.example.com/screenshots_1", "www.example.com/screenshots_2"
    s.license          = 'MIT'
    s.author           = { "Me" =&gt; "me@awesomestuff.com" }
    s.source           = { :git =&gt; "https://awesome.com/awesome/my-custom-pod.git", :tag =&gt; s.version.to_s }
    s.social_media_url = 'https://twitter.com/awesomestuff'
  
    s.platform     = :ios, '8.0'
    s.requires_arc = true
  
    s.source_files = 'Pod/Classes/**/*'
    s.resource_bundles = {
      'my-custom-pod' =&gt; ['Pod/Assets/*.png']
    }
  
    # s.public_header_files = 'Pod/Classes/**/*.h'
    s.frameworks = 'CoreLocation', 'MapKit'
    s.dependency 'SSKeychain', '~&gt; 1.2.3'
    s.dependency 'FMDB', '~&gt; 2.5'
    s.dependency 'GoogleMaps', '~&gt; 1.10.4'
    s.dependency 'Socket.IO-Client-Swift', '~&gt; 4.0.4'
  end
  </code></pre>
  
  <p>Here, the socket io client is the issue. I'm able to import the socket io framework into my other ObjC projects no problem, but I've never tried to do it into a custom cocoa pod.</p>
  
  <p>Any help is much appreciated. Thanks in advance.</p>