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Everything should be made as simple as possible, but no simpler.

Vim for Programmers - Folding

This is a first post in a series of how Vim can make programmer’s life easier. Vim strikes a nice compromise between simple editor and monolithic IDEs. I find this tool very helpful during my day to day developers tasks. I don’t treat it as a replacement for my favorite IDE but rather as a supporting tool. In this post I would like to introduce folding - very nice and useful feature.

Folding

Folding lets you define which parts of the file you can see. For example in a method you can hide everything inside curly braces letting only definition of function be visible.

When you use fold command, Vim hides given text and leaves in its place a one-line placeholder. The hidden text now can be managed by this placeholder. In a screenshot above, you can spot four folded methods~(there are four one-line placeholders). The first one - fibonacci, consists of 15 rows, takes an int as a parameter and returns a long. There is no limit on how many folds you can create. You can even create folds within folds~(nested folds).

Vim offers six ways to create folds:

  • manual - using Vim commands
  • indent - corresponding to the text indentation
  • expr - define folds with regular expressions
  • syntax - based on the file’s language syntax
  • diff - a difference between two files define folds
  • marker

The fold commands

Command  
zA Toggle the state of folds, recursively
zC Close folds, recursively
zD Delete folds, recursively
zO Open folds, recursively
zE Eliminate all folds
zf Create a fold from the current line to the one where the following motion command takes a cursor
countzF Create a fold covering count lines, starting with the current line
zM Set option foldlevel to 0
zN, zn Set (zN) or reset (zn) the foldenable option
za Toggle the state of one fold
zc Close one fold
zd Delete one fold
zi Toggle the value of the foldenable option
zj ,zk Move cursor to the start (zj) of the fold or to the end (zk) of the previous fold
zm, zr Decrement (zm) or increment (zr) the value of the foldlevel option by one
zo Open one fold

Manual folding

Suppose we want to hide 3 lines of the if statement in a fold

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public static long fibonacci(int n) {

  if (n == 0 || n == 1) {
    return n;
  }

  return fibonacci(n - 1) + fibonacci(n - 2);

}

To do this just move cursor to the beginning of if statement and execute:

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3zf

The result should be similar to the one shown below

Let’s try more sofisticated command - fold block of code. Position the cursor over the beginning or ending brace of a block of code and type:

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zf%

There is a one thing to note. Character following zf command - % is a motion command that moves cursor to the matching brace.

To learn more about folding and generally about vim, I recommend to read Learning the Vi and Vim Editors

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