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Code or text folding, or less commonly holophrasting, is a feature of some graphical user interfaces that allows the user to selectively hide ("fold") or display ("unfold") parts of a document. This allows the user to manage large amounts of text while viewing only those subsections that are currently of interest. It is typically used with documents which have a natural
Code or text folding, or less commonly holophrasting, is a feature of some graphical user interfaces that allows the user to selectively hide ("fold") or display ("unfold") parts of a document. This allows the user to manage large amounts of text while viewing only those subsections that are currently of interest. It is typically used with documents which have a natural tree structure
A tree structure, tree diagram, or tree model is a way of representing the hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the classic representation resembles a tree, although the chart is genera ...
consisting of nested elements. Other names for these features include expand and collapse, code hiding, and outlining. In Microsoft Word
Microsoft Word is a word processor, word processing software developed by Microsoft. It was first released on October 25, 1983, under the name ''Multi-Tool Word'' for Xenix systems. Subsequent versions were later written for several other pla ...
, the feature is called "collapsible outlining".
Many user interfaces provide disclosure widgets for code folding in a sidebar, indicated for example by a triangle that points sideways (if collapsed) or down (if expanded), or by a /code> box for collapsible (expanded) text, and a /code> box for expandable (collapsed) text.
Code folding is found in text editor
A text editor is a type of computer program that edits plain text. Such programs are sometimes known as "notepad" software (e.g. Windows Notepad). Text editors are provided with operating systems and software development packages, and can be ...
s, source code editors, and IDEs. The folding structure typically follows the syntax tree Syntax tree may refer to:
* Abstract syntax tree, used in computer science
* Concrete syntax tree
A parse tree or parsing tree or derivation tree or concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a str ...
of the program defined by the computer language
A computer language is a formal language used to communicate with a computer. Types of computer languages include:
* Construction language – all forms of communication by which a human can specify an executable problem solution to a comput ...
. It may also be defined by levels of indentation, or be specified explicitly using an in-band marker (saved as part of the source code) or out-of-band.
Text folding is a similar feature used on ordinary text, where the nested elements consist of paragraphs, sections, or outline levels. Programs offering this include folding editor
Code or text folding, or less commonly holophrasting, is a feature of some graphical user interfaces that allows the user to selectively hide ("fold") or display ("unfold") parts of a document. This allows the user to manage large amounts of tex ...
s, outliners, and some word processor
A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features.
Early word processors were stand-alone devices dedicated to the function, but current ...
s.
Data folding is found in some hex editors and is used to structure a binary file or hide inaccessible data sections.
Folding is also frequently used in data comparison, to select one version or another, or only the differences.
History
The earliest known example of code folding in an editor is in NLS (computer system). Probably the first widely available folding editor was the 1974 Structured Programming Facility (SPF) editor for IBM 370 mainframes, which could hide lines based on their indentation. It displayed on character-mapped 3270 terminals. It was very useful for prolix languages like COBOL
COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily u ...
. It evolved into the Interactive System Productivity Facility (ISPF
In computing, Interactive System Productivity Facility (ISPF) is a software product for many historic IBM mainframe operating systems and currently the z/OS and z/VM operating systems that run on IBM mainframes. It includes a screen editor, th ...
).
Use
Code folding has various use patterns, primarily organizing code or hiding less useful information so one can focus on more important information. Common patterns follow.
Outlining
Most basically, applications use code folding to outline source code, collapsing each block to a single line. This can be only top-level blocks like functions and classes, nested blocks like nested functions and methods, or all blocks, notably control-flow blocks. This allows one to get an overview of code, easily navigating and rearranging it, and to drill down into more detail as needed, without being distracted by other code. Viewing-wise, this allows one to quickly see a list of all functions (without their bodies), while navigation-wise this replaces extensive paging past long functions – or searching for the target – with going directly to the next function.
Hiding boilerplate code
Some languages or libraries require extensive boilerplate code
In computer programming, boilerplate code, or simply boilerplate, are sections of code that are repeated in multiple places with little to no variation. When using languages that are considered ''verbose'', the programmer must write a lot of boile ...
. This results in extremely long code, which can obscure the main point. Further, substantive code can be lost in the boilerplate.
For example, in Java a single private field with a getter and setter requires at least 3 lines, if each is on a separate line:
private String name = null;
public String getName()
public void setName(String name)
This expands to 10 lines with conventional function line breaks and spacing between functions (including trailing newline):
private String name = null;
public String getName()
public void setName(String name)
Documentation with Javadoc expands this to 20 lines:
/**
* Property name readable/writable.
*/
private String name = null;
/**
* Getter for property name
*/
public String getName()
/**
* Setter for property name.
* @param name
*/
public void setName(String name)
If there are many such fields, the result can easily be hundreds of lines of code with very little "interesting" content – code folding can reduce this to a single line per field, or even to a single line for all fields. Further, if all routine fields are folded, but non-routine fields (where getter or setter is not just returning or assigning a private field) are not folded, it becomes easier to see the substantive code.
Collapsing metadata
Metadata can be lengthy, and is generally less important than the data it is describing. Collapsing metadata allows one to primarily focus on the data, not the metadata. For example, a long list of attributes in C# may be manually collapsed as follows:
#region Attributes
rowsable(false) ergableProperty(false) efaultValue(null) ersistenceMode(PersistenceMode.InnerProperty) emplateContainer(typeof(MyType)) emplateInstance(TemplateInstance.Single)
#endregion
public ITemplate ContentTemplate
The resulting code displays as:
Attributes
public ITemplate ContentTemplate
Collapsing comments
Comments are a form of human-readable metadata, and lengthy comments can disrupt the flow of code. This can be the case either for a long comment for a short section of code, such as a paragraph to explain one line, or comments for documentation generators, such as Javadoc o
XML Documentation
Code folding allows one to have long comments, but to display them only when required. In cases where a long comment has a single summary line, such as Python docstrings, the summary can still be displayed when the section is collapsed, allowing a summary/detailed view.
Showing structure or sandwich code in structured programming
Structured programming
Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection ( if/then/else) and repetition ( ...
consists of nested blocks of code, and long blocks of code – such as long switch statements – can obscure the overall structure. Code folding allows one to see the overall structure and expand to a specific level. Further, in some uses, particularly strict structured programming (single function exit), there are code patterns that are hard to see when looking at expanded code. For example, in resource management
In organizational studies, resource management is the efficient and effective development of an organization's resources when they are needed. Such resources may include the financial resources, inventory, human skills, production resources, or ...
in structured programming, one generally acquires a resource, followed by a block of code using the resource, and finishing with releasing the resource. The acquisition/release pairing is hard to see if there is a long block of code in between, but easy to see if the intervening block is folded. Similarly, in conditional code like if...then...else, secondary blocks may be far from the condition statement.
Grouping code
Fold groups can be used to group code, either by explicit grouping – similar to comment blocks separating a module into sections, or class members into associated groups – or implicitly, such as by automatically grouping class members by access level.
Hiding legacy code
Legacy code – or any code that a developer does not wish to view or change at a given point in time – can be folded away so that programmers can concentrate on the code under consideration.
Hiding in-source data tables
Conventions
In order to support code folding, the text editor must provide a mechanism for identifying "folding points" within a text file. Some text editors provide this mechanism automatically, while others provide defaults that can either be overridden or augmented by the user.
There are various mechanisms, coarsely divided as automatic and manual – do they require any specification by the programmer? Folding points are usually determined with one or more of the following mechanisms. Each of these has its own distinct advantages and difficulties, and it is essentially up to the developers who create the text editor software to decide which to implement. Text editors that provide support for multiple folding mechanisms typically allow the user to choose which is most appropriate for the file being edited.
Syntax-dependent
Syntax-dependent folding points are those that rely on the content of the file being edited in order to specify where specific folding regions should begin and end. Syntax-based folding points are typically defined around any or all of the standard sub-features of the markup language
Markup language refers to a text-encoding system consisting of a set of symbols inserted in a text document to control its structure, formatting, or the relationship between its parts. Markup is often used to control the display of the document ...
or programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
in use. These are desirable due to being automatic and agreeing with code structure, but may require significant work to implement, and time to compute when editing a file.
Indentation-based
Indentation-based folding points are generally specified by the position and sequence of non-printing whitespace, such as tabs and spaces, within the text. This is most often used as a simple form of syntax-based folding, as indentation almost always reflects nesting level in indent style
In computer programming, an indentation style is a convention governing the indentation of blocks of code to convey program structure. This article largely addresses the free-form languages, such as C and its descendants, but can be (and oft ...
s for structured programming languages.
This convention is particularly suitable to syntaxes that have an off-side rule, so the structure largely agrees with the indent. Examples include Python and text files that require indentation as a rule by themselves. However, even in these cases, structure does not exactly agree with indent, such as in line continuation, and thus syntax-dependent folding is preferred.
Token-based
Token-based folding points are specified using special delimiter
A delimiter is a sequence of one or more characters for specifying the boundary between separate, independent regions in plain text, mathematical expressions or other data streams. An example of a delimiter is the comma character, which acts a ...
s that serve no other purpose in the text than to identify the boundaries of folding points. This convention can be compared to indentation-based folding points, where printable characters are used instead of whitespace. The most common delimiter tokens are #region
/code>
C# directives
, respectively #Region
/code>
Visual Basic directives
, used in Microsoft Visual Studio
Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs including websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platforms such ...
Code Editor. These are treated syntactically as compiler directives
In computer programming, a directive or pragma (from "pragmatic") is a language construct that specifies how a compiler (or other translator) should process its input. Directives are not part of the grammar of a programming language, and may vary ...
, though they do not affect compilation.
As a manual method, token-based folding allows discretion in grouping code based on arbitrary criteria, such as "functions related to a given task", which cannot be inferred from syntactic analysis.
Token-based folding requires in-band signalling, with folding tokens essentially being structured comments, and unlike other methods, are present in the source code and visible to other programmers. This allows them to be shared, but also requires their use (or preservation) by all programmers working on a particular file, and can cause friction and maintenance burden.
User-specified
User-specified folding allows the user to fold sections of text using a generic selection method, but without changing the source code (out-of-band), instead being specified only in the editor. For example, a programmer may select some lines of text and specify that they should be folded. Folded text might be anonymous or named, and this may be preserved across editing sessions or discarded. Unlike token-based folding, this does not change the source text – it thus is not shared with other editors of the file, and is not visible in the code.
Examples
The following document contains folding tokens (
Heading 1
Heading 2
Heading 3
When loaded into a folding editor, the outline structure will be shown:
Heading 1
{{{ ...
Heading 2
{{{ ...
Heading 3
{{{ ...
Usually clicking on the {{{
Software with code folding capability
One of the earliest folding editors was STET, an editor written for the VM/CMS
VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers.
The following ver ...
operating system in 1977 by Mike Cowlishaw
Mike Cowlishaw is a visiting professor at the Department of Computer Science at the University of Warwick, and a Fellow of the Royal Academy of Engineering. He is a retired IBM Fellow, and was a Fellow of the Institute of Engineering and Techn ...
. STET is a text editor (for documentation, programs, etc.) which folds files on the basis of blocks of lines; any block of lines can be folded and replaced by a name line (which in turn can be part of a block which itself can then be folded).
A folding editor appeared in the occam IDE ''circa'' 1983, which was called the Inmos Transputer Development System (TDS),. The "f" editor (in list below) probably is the most intact legacy from this work.
The Macintosh
The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
computer historically had a number of source code editors that "folded" portions of code via " disclosure triangles". The UserLand Software product Frontier is a scripting environment that has this capability.
Folding is provided by many modern text editors, and syntax-based or semantics-based folding is now a component of many software development environments. Editors include:
{, class="wikitable sortable" style="text-align: center; width: auto; table-layout: fixed;"
, -
! style="width: 12em" , Name
! Token
! Indentation
! Syntax
! User
, -
, ABAP Editor
, {{yes
, {{dunno
, {{yes
, {{dunno
, -
, AkelPad
, {{dunno
, {{dunno
, {{yes
, {{dunno
, -
, Anjuta IDE
, {{dunno
, {{yes
, {{yes
, {{dunno
, -
, Atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, a ...
{{efn, http://flight-manual.atom.io/using-atom/sections/folding/
, {{dunno
, {{yes
, {{dunno
, {{yes
, -
, BBEdit
, {{dunno
, {{dunno
, {{Yes
, {{dunno
, -
, Brackets
A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'r ...
, {{yes2Plug-in
, {{yes
, {{yes
, {{no
, -
, Codeanywhere
, {{yes
, {{yes
, {{yes
, {{dunno
, -
, Codenvy
, {{yes
, {{yes
, {{yes
, {{dunno
, -
, Code::Blocks IDE
, {{Yes
, {{Yes
, {{Yes
, {{Yes
, -
, Cubic IDE
, {{Yes
, {{Yes
, {{Yes
, {{Yes
, -
, CudaText
CudaText, from Bosnian-Croatian-Montenegrin-Serbian ''čuda'' ("wonders" or "miracles", IPA: �uda, is a free open source cross-platform native GUI text and source code editor. CudaText supersedes its predecessor ''SynWrite'', no longer under ...
, {{dunno
, {{dunno
, {{dunno
, {{dunno
, -
, Delphi IDE
, {{Yes
, {{dunno
, {{Yes
, {{dunno
, -
, Dreamweaver
Adobe Dreamweaver is a proprietary web development tool from Adobe Inc. It was created by Macromedia in 1997 and developed by them until Macromedia was acquired by Adobe Systems in 2005.
Adobe Dreamweaver is available for the macOS and Windo ...
, {{dunno
, {{dunno
, {{dunno
, {{yes
, -
, Eclipse
An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three c ...
, {{dunno
, {{dunno
, {{yes
, {{dunno
, -
, EditPlus
, {{no
, {{yes
, {{no
, {{no
, -
, Emacs
Emacs , originally named EMACS (an acronym for "Editor MACroS"), is a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as "the extensible, customizable, ...
, {{yes{{efn, Token-based folding is implemented by th
''folding'' minor mode
One can also use
' and
allout
' minor modes for sectioning program sources.
, {{dunno{{efn, One can use the set-selective-display function in Emacs to hide lines based on the indentation level, as suggested in th
Universal code folding
note.
, {{yes{{efn, 1=Syntax-dependent folding is supported by the
' and
allout
' modes
for special dedicated outline-syntaxes; by the
hideshow
' minor mode for some programming languages; also, by the
semantic-tag-folding
' minor mode and the senator-fold-tag
/code> command fo
syntaxes supported by ''semantic'' (a component of CEDET)
as well as by
doc-mode
' for JavaDoc or Doxygen comments, by
TeX-fold-mode
',
/code> command,
nxml-outln
' library in the corresponding language-specific modes, and possibly in other modes for particular syntaxes. Sometimes, the standard simple ''outline'' minor mode is used to simulate syntax-based folding, cf. th
use
of it in properly indented Emacs Lisp source code, th
use of it (see near the end of the page)
for properly indented HTML. Several folding mechanisms are unified by the
fold-dwim
' interface. See als
CategoryHideStuff
, {{yes{{efn, Folding of user-selected regions in Emacs is implemented by the hide-region-hide
/code> command.
, -
, EmEditor Professional
, {{dunno
, {{yes
, {{yes
, {{dunno
, -
, FlashDevelop IDE
, {{dunno
, {{dunno
, {{yes
, {{dunno
, -
, geany
, {{dunno
, {{yes
, {{yes
, {{dunno
, -
, gedit
, {{yes
, {{yes
, {{yes
, {{dunno
, -
, ISPF
In computing, Interactive System Productivity Facility (ISPF) is a software product for many historic IBM mainframe operating systems and currently the z/OS and z/VM operating systems that run on IBM mainframes. It includes a screen editor, th ...
, {{dunno
, {{Yes
, {{dunno
, {{Yes
, -
, JED
, {{yes
, {{yes{{efn, The set_selective_display function may be used to hide lines indented beyond a specified amount.
, {{dunno
, {{no
, -
, jEdit
, {{yes
, {{yes
, {{yes
, {{yes
, -
, Kate
, {{yes
, {{yes
, {{yes
, {{yes
, -
, MATLAB
MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementat ...
, {{no
, {{no
, {{yes
, {{no
, -
, MS Visual Studio
, {{yes
, {{yes
, {{yes
, {{yes
, -
, NetBeans IDE
NetBeans is an integrated development environment (IDE) for Java. NetBeans allows applications to be developed from a set of modular software components called ''modules''. NetBeans runs on Windows, macOS, Linux and Solaris. In addition to Java ...
, {{yes
, {{yes
, {{yes
, {{yes
, -
, Notepad++
Notepad++ is a text and source code editor for use with Microsoft Windows. It supports tabbed editing, which allows working with multiple open files in a single window. The product's name comes from the C postfix increment operator.
Notepad ...
, {{dunno
, {{yes
, {{yes
, {{yes
, -
, NuSphere PHPEd
, {{dunno
, {{dunno
, {{Yes
, {{Yes
, -
, Qt Creator
, {{dunno
, {{dunno
, {{Yes
, {{dunno
, -
, SciTE
SciTE or SCIntilla based Text Editor is a cross-platform text editor written by Neil Hodgson using the Scintilla editing component. It is licensed under a minimal version of the Historical Permission Notice and Disclaimer.
Lightweight and buil ...
, {{yes
, {{yes
, {{yes
, {{dunno
, -
, STET{{efn, STET may have been the first text editor that supported folding{{Citation needed, date=January 2008
, {{dunno
, {{dunno
, {{dunno
, {{dunno
, -
, TextMate
, {{yes
, {{yes
, {{yes
, {{yes
, -
, UltraEdit
UltraEdit is a commercial text editor for Microsoft Windows, Linux and OS X created in 1994 by the founder of IDM Computer Solutions Inc., Ian D. Mead, and owned by Idera, Inc. since August 2021. The editor contains tools for programmers, includ ...
, {{no
, {{no
, {{yes
, {{Yes
, -
, Vim
, {{yes
, {{yes
, {{yes
, {{yes
, -
, Visual Expert
Visual Expert is a static code analysis tool, extracting design and technical information from software source code by reverse-engineering, used by programmers for software maintenance, modernization or optimization.
It is designed to parse seve ...
, {{dunno
, {{dunno
, {{yes
, {{dunno
, -
, Visual Studio Code
, {{yes
, {{yes
, {{yes
, {{no
, -
, Xcode
Xcode is Apple's integrated development environment (IDE) for macOS, used to develop software for macOS, iOS, iPadOS, watchOS, and tvOS. It was initially released in late 2003; the latest stable release is version 14.2, released on December 13, ...
, {{yes
, {{yes
, {{yes
, {{yes
, -
, Zend Studio
Zend Studio is a commercial, proprietary integrated development environment (IDE) for PHP developed by Zend Technologies, based on the PHP Development Tools (PDT) plugin for the Eclipse platform (the PDT project is led by Zend).
Zend Studio is t ...
, {{dunno
, {{dunno
, {{dunno
, {{dunno
Other editors
{{div col, colwidth=22em
* aoeui, the Dvorak-optimized editor
* Author-it enterprise authoring and component content management software
* Bluefish
The bluefish (''Pomatomus saltatrix'') is the only extant species of the family Pomatomidae. It is a marine pelagic fish found around the world in temperate and subtropical waters, except for the northern Pacific Ocean. Bluefish are known as t ...
* f (alias xf, Winf, Winf32)
* Folding Text Editor
* GFA BASIC
* GridinSoft Notepad
* IntelliJ IDEA
IntelliJ IDEA is an integrated development environment (IDE) written in Java for developing computer software written in Java, Kotlin, Groovy, and other JVM-based languages. It is developed by JetBrains (formerly known as IntelliJ) and is av ...
(and other JetBrains' IDE)
* Keynote
A keynote in public speaking is a talk that establishes a main underlying theme. In corporate or commercial settings, greater importance is attached to the delivery of a keynote speech or keynote address. The keynote establishes the framework fo ...
* Komodo Edit
* Kwrite
* Leo
* LEXX/LPEX (editor for the OED)LEXX – A programmable structured editor ''IBM Journal of Research and Development'', Vol 31, No. 1, 1987, IBM Reprint order number G322-0151
* MonoDevelop
* NoteTab Pro
* Padre
* RJ Text Editor
* Smultron
Smultron is a text editor for macOS that is designed for both beginners and advanced users, named after the Swedish word for the woodland strawberry.
It was originally published as free software but is now sold through the Mac App Store. It i ...
* The Hessling Editor
* Visual Studio
Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs including web site, websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platfor ...
* WinShell (since version 3.30)
* XEDIT (however its folding is effected by scripts)
* Zeus
{{div col end
See also
*The Programming features section of the Comparison of text editors article for more editors that support folding
* Accordion (GUI), a similar UI technique applied to hierarchical lists rather than text
Notes
{{notelist
References
{{reflist
{{refbegin
* {{cite web, url=http://www.codinghorror.com/blog/2008/07/the-problem-with-code-folding.html , title=The Problem With Code Folding , first=Jeff , last=Atwood , authorlink=Jeff Atwood , work=Coding Horror , date=6 Jul 2008, postscript= – criticism of code folding, detailed comments on use.
{{refend
External links
{{Commons category
What is a folding editor?
by the author of the fe
/code> editor.
Description of the folding editor
used in occam.
{{DEFAULTSORT:Code Folding
Source code
Text editor features
Articles with example C Sharp code