How do I duplicate a whole line in Emacs?

Question

I saw this same question for VIM and it has been something that I myself wanted to know how to do for Emacs. In ReSharper I use CTRL-D for this action. What is the least num

Answer 1

This functionality should match up with JetBrains' implementation in terms of duplicating both by line or region, and then leaving the point and/ or active region as expected:

Just a wrapper to around the interactive form:

(defun wrx/duplicate-line-or-region (beg end)
  "Implements functionality of JetBrains' `Command-d' shortcut for `duplicate-line'.
   BEG & END correspond point & mark, smaller first
   `use-region-p' explained: 
   http://emacs.stackexchange.com/questions/12334/elisp-for-applying-command-to-only-the-selected-region#answer-12335"
  (interactive "r")
  (if (use-region-p)
      (wrx/duplicate-region-in-buffer beg end)
    (wrx/duplicate-line-in-buffer)))

Which calls this,

(defun wrx/duplicate-region-in-buffer (beg end)
  "copy and duplicate context of current active region
   |------------------------+----------------------------|
   |        before          |           after            |
   |------------------------+----------------------------|
   | first line here  | first line here            |
   | second item now | second itemline here |
   |                        | second item now     |
   |------------------------+----------------------------|
   TODO: Acts funky when point < mark"
  (set-mark-command nil)
  (insert (buffer-substring beg end))
  (setq deactivate-mark nil))

Or this

(defun wrx/duplicate-line-in-buffer ()
  "Duplicate current line, maintaining column position.
   |--------------------------+--------------------------|
   |          before          |          after           |
   |--------------------------+--------------------------|
   | lorem ipsum dolor | lorem ipsum dolor        |
   |                          | lorem ipsum dolor |
   |--------------------------+--------------------------|
   TODO: Save history for `Cmd-Z'
   Context: 
   http://stackoverflow.com/questions/88399/how-do-i-duplicate-a-whole-line-in-emacs#answer-551053"
  (setq columns-over (current-column))
  (save-excursion
    (kill-whole-line)
    (yank)
    (yank))
  (let (v)
    (dotimes (n columns-over v)
      (right-char)
      (setq v (cons n v))))
  (next-line))

And then I have this bound to meta+shift+d

(global-set-key (kbd "M-D") 'wrx/duplicate-line-or-region)