How to duplicate a whole line in Vim?

Question

How do I duplicate a whole line in Vim in a similar way to Ctrl+D in IntelliJ IDEA/ Resharper or Ctrl+Alt+&

Answer 1

I know I'm late to the party, but whatever; I have this in my .vimrc:

nnoremap  :copy .
vnoremap  :copy '>

the :copy command just copies the selected line or the range (always whole lines) to below the line number given as its argument.

In normal mode what this does is copy . copy this line to just below this line.

And in visual mode it turns into '<,'> copy '> copy from start of selection to end of selection to the line below end of selection.