title: Replace old Objective-c library by new Swift one in several apps
body: <p>I have an old library in objective C, developped by several people following (one stop and the next continue the project...).
  This library is used in several applications, most of them developped in objective C.
  I want to add new features in this app, but the code is not maintainable actually (no tests, no comment, etc...). </p>
  
  <p>My main idea was to rebuild a framework or library in Swift. I have the business requirement but I'm not comfortable with objective c.</p>
  
  <p>Am I going to have compatibility problems if I want to use my new swift library in "old" objective C application, or It could be great If I don't change the API? </p>
  
  <p>Could it be transparent for the client who have his own application and have to use the new library now? </p>