Opening a new line without returning the carriage

Question

Say I want to begin letters like this:

Dear world,
           hello.

What's the simplest way to define a mapping that opens a new line preserving the cursor's horizontal position?

Answer 1

An easy way to achieve this using no vimscript is the following:

nnoremap <leader>o yyp^v$r A

This assumes you want to start the mapping in normal mode (otherwise just add <Esc> to the beginning of your insert mode mapping). It copies the current line with yy, pastes it on the line below (p), selects the pasted text in visual mode (^v$), replaces the selection with whitespaces (r followed by a space) and jumps to the end, putting you in insert mode (A).