How to achieve code folding effects in Emacs?

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What's the best way to achieve something like code folding, or the type of cycling that org-mode uses. What would be the best solution in elisp to create this type of behavior?

EDIT: I'm sorry I was not clear. I want to program something in elisp that does things very similar to code folding, or actually most like org-mode with the hierarchy that can be expanded. I am wondering the best way to achieve this effect. I think I have heard emacs overlays are a good solution, but I don't know.

As far as folding I just use the builtin set-selective-display

EDIT NUMBER 2:

Thanks for the answers but I think I am asking the wrong question so let me try to be more clear on what I am trying to do. I would like to create the following

When you put your point on a function and call this elisp function it will put the function definition from wherever it is (I am thinking of just using find-tag for this) and unfold it in the current buffer. The idea is if you have to jump to a different buffer to read the function definition I feel like it's a context switch to another file. So I would like it to behave like code folding only it pulls in code external from the buffer. This presents some problems as it can not actually paste the code into the buffer or if someone saves it will save the pulled in code. So I am wondering if there is a way to create an area inside a buffer that is also not part of the buffer. I think that makes sense.

Settling answered 6/7, 2009 at 2:29 Comment(3)

You're looking for something that when you call it with point in a function CALL it jumps to the function definition? sort of like getting help about an elisp function will let you jump to the elisp code? I don't think you can do this without some concept of "The project" For example, how would you know which "swap" function you want to jump to? – Romanticism 30/7, 2009 at 19:12

See also: #383281 where selective-display is tweaked a bit for some folding-like effects. – Forbade 17/2, 2010 at 14:31

I recommend you remove your EDIT NB 2 and make a new question for it. – Winch 8/6, 2017 at 13:9

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Folding is generally unnecessary with emacs, as it has tools that explicitly implement the actions people do manually when folding code.

Most people have good success with simple incremental searches. See "foo" mentioned somewhere? Type C-sfoo, find the definition, press enter, read it, and then press C-x C-x to go back to where you were. Simple and very useful.

Most modes support imenu. M-ximenu will let you jump to a function definition (etc.) by name. You can also bind it to a mouse click to get a menu of functions (or add it to the menubar; see the Info page for more detail). It provides data for which-function-mode, which will let you see which function you are currently inside in the modeline. (Why are your functions this long, though?)

There is also speedbar, which displays the imenu information (and other things) graphically.

If you want to get an overview of your file, try M-xoccur". Given a regex, it will create a new buffer with each match in the current buffer. You can search for "(defun" to get an overview of the functions the current file implements. Clicking on the result will move you to that position in the file.

So anyway, think about what you really want to achieve, and Emacs probably implements that. Don't fight with imperfect tools that make you fold and unfold things constantly.

Falsity answered 31/7, 2009 at 8:35 Comment(8)

Vim also provides all of these features in one form or another but I still find its code folding facility invaluable. – Erma 30/3, 2011 at 18:19

M-x occur just saved me a bunch of headache. Excellent post! – Wipe 24/8, 2011 at 5:32

I down-voted for the first sentence ("Folding is generally unnecessary with emacs, as..."). I use simple folding (based on indent level) constantly to scan the structure of unfamiliar code. – Mitzimitzie 17/11, 2011 at 16:33

M-s o is the shortcut for M-x occur – Bloater 23/1, 2013 at 0:11

I up-voted because many useful shortcut in the answer but also up-voted @SimonMichael comment because fold / unfold could still be useful sometimes ! – Twophase 14/2, 2013 at 22:13

The answer was well thought out and very informative. However, the OP asked how to do code folding. The OP did not ask what everyone's favorite way of avoiding code folding was. Down voted. – Cheston 16/5, 2013 at 18:11

It is true that the question was about folding. But what @Falsity wants to say is that folding is way of using, to people that aren't aware of all that emacs can offer. he gives the extra mile, and i don't think anyone needs to down vote him for that, on contrary. – Kep 4/12, 2019 at 16:10

Folding is useful when looking at how the code before a block relates to the code after the block, for example when checking to see that elements that must be paired are paired properly. All the techniques listed above have a place, and so does folding. – Ultramontanism 30/9, 2023 at 14:19

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You can use the hide-show mode (hs-minor-mode). To activate this mode on the fly for the current buffer only, type M-x hs-minor-mode RET

Assuming you have the default keybinding:

C-c @ C-M-h To fold it all (hs-hide-all).
C-c @ C-h Hides the current block (hs-hide-block). The point (cursor) has to be inside the block.
C-c @ C-s Show current block (hs-show-block). The point has to be in the {...} marker that is hiding the code.

Statampere answered 30/7, 2009 at 19:18 Comment(3)

This works well. And with evil-mode, this is triggered by the normal vim commands: zR, zM, zo, zc. – Underbodice 9/12, 2013 at 15:13

Should be the accepted answer, this is THE way to code folding in emacs. Works very well everywhere and built-in. – Fabliau 11/8, 2023 at 8:38

For me this really fails with Python. I had a class that was about 80 lines and then below that I had another 100 lines of code that all got folded when trying to fold the class so this was a bit more aggressive then I would have liked. – Related 27/2 at 17:38