1. Install

   (require 'docsetutil)

2. You may consider binding docsetutil-api to a key, for example:

   (define-key help-map "d" 'docsetutil-api) ; C-h d

3. Choose a docset to use:

   M-x docsetutil-choose-docset

4. API search with completion:

   M-x docsetutil-api

5. API browse

   M-x docsetutil-browse-api

6. Full text search:

   M-x docsetutil-fulltext

Function docsetutil-completions provides a decent source for objc/swift completion. It is not true code completion but extremely fast and can save you a lot of typing. Improvement expected in this area.

If you use hippie-expand, you may want to add try-docsetutil-completions to hippie-expand-try-functions-list

(setq hippie-expand-try-functions-list
      '(try-expand-dabbrev
        try-expand-dabbrev-all-buffers
        try-docsetutil-completions
        try-expand-dabbrev-from-kill
        try-expand-line
        try-complete-lisp-symbol-partially
        try-complete-lisp-symbol
        try-complete-file-name-partially
        try-complete-file-name
        try-expand-whole-kill))

When you first run docsetutil-api, docsetutil-browse-api or docsetutil-fulltext, it may take a few seconds to build the completion table, which is then cached to disk in the directory docsetutil-cache-directory.