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Introduce variable

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Tip 1171 Printable Monobook Previous Next

created 2006 · complexity basic · author Alan Brogan · version 5.7

The following is from my vimrc, and works as a simple "introduce variable". It is sufficient for Python, but for typed languages (e.g. C++, Java) you will need to add a type (int, String, etc) to the start of the new line.

" map \v to put x = y on the line above cursor, where
" x is the last text inserted
" y is the last text deleted
map <Leader>v 0wh:put .<CR>a = <Esc>pa<CR><Esc>

Example, given (Python) source code like:

if x > 3 * y + 4 * z:

You could position the cursor on the 3, then delete the RHS formula, and insert a name for it. You can do the "delete and insert" separately or in one go, e.g. go to the 3 and press "c/:<Cr>formula<Esc>". Or separately as "d/:<Cr>", followed by "iformula<Esc>". In either case you should now see:

if x > formula:

Then pressing \v gives

formula = 3 * y + 4 * z
if x > formula:

What it does:

  1. Go to start of line
  2. Go to before next word
  3. Add the last inserted text
  4. Add " = "
  5. Add the last deleted text
  6. Add a <Cr> to separate the new line from the old line (and vim preserves the indentation)


Note that the " register has your last edit and in insert mode, <C-R> will paste the contents of the register indicated by the next keystroke, so your example re-interpreted with standard commands is:

(positioned on 3)
ct:formula<C-o>Oformula = <C-r>"<Esc>

ct: - change to the colon
<C-o>O - break out of insert for one command and Open a line above (<Esc>O would work fine, but <Esc> is so far away...)
<C-r>" - paste the contents of the unnamed register (:h "")

Your re-interpretation is one step short, in that you type in the new name twice. The original starts after the new name is typed in, so closer would be :

map <Leader>v O<C-r>. = <C-r>"<Esc>

See also VimTip589 which is also about refactoring.

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