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{{Short description|Organizing code into modules}}
{{Programming paradigms}}▼
{{More citations needed|date=June 2022}}
'''Modular programming''' is a [[software development]] mindset that emphasizes organizing the [[function (programming)|functions]] of a [[codebase]] into independent modules {{endash}} each providing an [[Separation of concerns|aspect]] of a [[computer program]] in its entirety without providing other aspects.
A module [[
▲A module [[interface (computing)|interface]] expresses the elements that are provided and required by the module. The elements defined in the interface are detectable by other modules. The [[implementation]] contains the working code that corresponds to the elements declared in the interface. Modular programming is closely related to [[structured programming]] and [[object-oriented programming]], all having the same goal of facilitating construction of large software programs and systems by [[Decomposition_(computer_science)|decomposition]] into smaller pieces, and all originating around the 1960s. While the historical usage of these terms has been inconsistent, "modular programming" now refers to the high-level decomposition of the code of an entire program into pieces: structured programming to the low-level code use of structured [[control flow]], and object-oriented programming to the ''data'' use of [[Object (computer science)|objects]], a kind of [[data structure]].
In object-oriented programming, the use of interfaces as an architectural pattern to construct modules is known as [[interface-based programming]].{{citation needed|date=June 2015}}
==History==▼
Modular programming, in the form of subsystems (particularly for I/O) and software libraries, dates to early software systems, where it was used for [[code reuse]]. Modular programming per se, with a goal of modularity, developed in the late 1960s and 1970s, as a larger-scale analog of the concept of [[structured programming]] (1960s). The term "modular programming" dates at least to the National Symposium on Modular Programming, organized at the Information and Systems Institute in July 1968 by [[Larry Constantine]]; other key concepts were [[information hiding]] (1972) and [[separation of concerns]] (SoC, 1974).▼
Modules were not included in the original specification for [[ALGOL 68]] (1968), but were included as extensions in early implementations, [[ALGOL 68-R]] (1970) and [[ALGOL 68C]] (1970), and later formalized.<ref>{{cite journal |last=Lindsey |first=Charles H. |author-link=Charles H. Lindsey |date=Feb 1976 |title=Proposal for a Modules Facility in ALGOL 68 |url=http://archive.computerhistory.org/resources/text/algol/ACM_Algol_bulletin/1061719/p19-lindsey.pdf |url-status=dead |journal=ALGOL Bulletin |issue=39 |pages=20–29 |archive-url=https://web.archive.org/web/20160303230037/http://archive.computerhistory.org/resources/text/algol/ACM_Algol_bulletin/1061719/p19-lindsey.pdf |archive-date=2016-03-03 |access-date=2014-12-01}}</ref> One of the first languages designed from the start for modular programming was the short-lived [[Modula]] (1975), by [[Niklaus Wirth]]. Another early modular language was [[Mesa (programming language)|Mesa]] (1970s), by [[Xerox PARC]], and Wirth drew on Mesa as well as the original Modula in its successor, [[Modula-2]] (1978), which influenced later languages, particularly through its successor, [[Modula-3]] (1980s). Modula's use of dot-[[qualified name]]s, like <code>M.a</code> to refer to object <code>a</code> from module <code>M</code>, coincides with notation to access a field of a record (and similarly for attributes or methods of objects), and is now widespread, seen in [[C++]], [[C Sharp (programming language)|C#]], [[Dart (programming language)|Dart]], [[Go (programming language)|Go]], [[Java (programming language)|Java]], [[OCaml]], and [[Python (programming language)|Python]], among others. Modular programming became widespread from the 1980s: the original [[Pascal (programming language)|Pascal]] language (1970) did not include modules, but later versions, notably [[UCSD Pascal]] (1978) and [[Turbo Pascal]] (1983) included them in the form of "units", as did the Pascal-influenced [[Ada (programming language)|Ada]] (1980). The Extended Pascal ISO 10206:1990 standard kept closer to Modula2 in its modular support. [[Standard ML]] (1984)<ref>{{cite
In the 1980s and 1990s, modular programming was overshadowed by and often conflated with [[object-oriented programming]], particularly due to the popularity of C++ and Java. For example, the C family of languages had support for [[Object (computer science)|objects]] and [[Class (computer programming)|classes]] in C++ (originally [[C with Classes]], 1980) and Objective-C (1983), only supporting modules 30 years or more later. Java (1995) supports modules in the form of [[Package manager|packages]], though the primary unit of code organization is a class. However, Python (1991) prominently used both modules and objects from the start, using modules as the primary unit of code organization and "packages" as a larger-scale unit; and [[Perl 5]] (1994) includes support for both modules and objects, with a vast array of modules being available from [[CPAN]] (1993). [[OCaml]] (1996) followed ML by supporting modules and functors.▼
Modular programming is now widespread, and found in virtually all major languages developed since the 1990s. The relative importance of modules varies between languages, and in class-based object-oriented languages there is still overlap and confusion with classes as a unit of organization and encapsulation, but these are both well-established as distinct concepts.▼
==Terminology==
The term
Furthermore, the term "package" has other uses in software (for example
Other terms for modules include
==Language support==
Languages that formally support the module concept include [[Ada (programming language)|Ada]], [[ALGOL
In the Java programming language, the term "package" is used for the analog of modules in the JLS;<ref>James Gosling, Bill Joy, Guy Steele, Gilad Bracha, ''The Java Language Specification, Third Edition'', {{ISBN|0-321-24678-0}}, 2005. In the Introduction, it is stated "Chapter 7 describes the structure of a program, which is organized into packages similar to the modules of Modula." The word "module" has no special meaning in Java.</ref> — see [[Java package]]. "[[Java Module System|Modules]]", a kind of set of packages, were introduced in [[Java 9]] as part of [http://openjdk.java.net/projects/jigsaw/ Project Jigsaw]; these were earlier called "superpackages" were planned for Java 7.
Conspicuous examples of languages that lack support for modules are [[C (programming language)|C]] and have been [[C++]] and Pascal in their original form, [[C (programming language)|C]] and [[C++]] do, however, allow separate compilation and declarative interfaces to be specified using [[header file]]s. Modules were added to Objective-C in [[iOS 7]] (2013); to C++ with [[C++20]],<ref>{{cite web|url=https://isocpp.org/files/papers/n4720.pdf|title=N4720: Working Draft, Extensions to C++ for Modules}}</ref> and Pascal was superseded by Modula and Oberon, which included modules from the start, and various derivatives that included modules. [[JavaScript]] has had native modules since [[ECMAScript]] 2015.▼
▲Conspicuous examples of languages that lack support for modules are [[C (programming language)|C]] and have been [[C++]] and Pascal in their original form, [[C (programming language)|C]] and [[C++]] do, however, allow separate compilation and declarative interfaces to be specified using [[header file]]s. Modules were added to Objective-C in [[iOS 7]] (2013); to C++ with [[C++20]],<ref>{{cite web|url=https://isocpp.org/files/papers/n4720.pdf|title=N4720: Working Draft, Extensions to C++ for Modules}}</ref> and Pascal was superseded by [[Modula]] and [[Oberon (programming language)|Oberon]], which included modules from the start, and various derivatives that included modules. [[JavaScript]] has had native modules since [[ECMAScript]] 2015. [[Modules (C++)|C++ modules]] have allowed backwards compatibility with headers (with "header units"). Dialects of C allow for modules, for example [[Clang]] supports [[Modules (C++)#Clang C modules|modules for the C language]],<ref>{{Cite web|url=https://clang.llvm.org/docs/Modules.html|title=Modules|website=clang.llvm.org}}</ref> though the syntax and semantics of Clang C modules differ from C++ modules significantly.
Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules, like, for example, in C. This is done by using existing language features, together with, for example, [[coding conventions]], [[programming idioms]] and the physical code structure. [[IBM i]] also uses modules when programming in the [[Integrated Language Environment]] (ILE).
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With modular programming, [[separation of concerns|concerns are separated]] such that modules perform logically discrete functions, interacting through well-defined interfaces. Often modules form a [[directed acyclic graph]] (DAG); in this case a cyclic dependency between modules is seen as indicating that these should be a single module. In the case where modules do form a DAG they can be arranged as a hierarchy, where the lowest-level modules are independent, depending on no other modules, and higher-level modules depend on lower-level ones. A particular program or library is a top-level module of its own hierarchy, but can in turn be seen as a lower-level module of a higher-level program, library, or system.
When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are written separately so when they are composed together, they construct the executable application program. Typically, these are also [[Compiler|compiled]] separately, via [[separate compilation]], and then linked by a [[Linker (computing)|linker]]. A [[Just-in-time compilation|just-in-time compiler]] may perform some of this construction "on-the-fly" at [[Run time (program lifecycle phase)|run time]].
These independent functions are commonly classified as either program control functions or specific task functions. Program control functions are designed to work for one program. Specific task functions are closely prepared to be applicable for various programs.
This makes modular designed systems, if built correctly, far more reusable than a traditional monolithic design, since all (or many) of these modules may then be reused (without change) in other projects. This also facilitates the "breaking down" of projects into several smaller projects. Theoretically, a modularized software project will be more easily assembled by large teams, since no team members are creating the whole system, or even need to know about the system as a whole. They can focus just on the assigned smaller task
▲==History==
▲Modular programming, in the form of subsystems (particularly for I/O) and software libraries, dates to early software systems, where it was used for [[code reuse]]. Modular programming per se, with a goal of modularity, developed in the late 1960s and 1970s, as a larger-scale analog of the concept of [[structured programming]] (1960s). The term "modular programming" dates at least to the National Symposium on Modular Programming, organized at the Information and Systems Institute in July 1968 by [[Larry Constantine]]; other key concepts were [[information hiding]] (1972) and [[separation of concerns]] (SoC, 1974).
▲}}</ref> One of the first languages designed from the start for modular programming was the short-lived [[Modula]] (1975), by [[Niklaus Wirth]]. Another early modular language was [[Mesa (programming language)|Mesa]] (1970s), by [[Xerox PARC]], and Wirth drew on Mesa as well as the original Modula in its successor, [[Modula-2]] (1978), which influenced later languages, particularly through its successor, [[Modula-3]] (1980s). Modula's use of dot-[[qualified name]]s, like <code>M.a</code> to refer to object <code>a</code> from module <code>M</code>, coincides with notation to access a field of a record (and similarly for attributes or methods of objects), and is now widespread, seen in C#, Dart, Go, Java, and Python, among others. Modular programming became widespread from the 1980s: the original [[Pascal (programming language)|Pascal]] language (1970) did not include modules, but later versions, notably [[UCSD Pascal]] (1978) and [[Turbo Pascal]] (1983) included them in the form of "units", as did the Pascal-influenced [[Ada (programming language)|Ada]] (1980). The Extended Pascal ISO 10206:1990 standard kept closer to Modula2 in its modular support. [[Standard ML]] (1984)<ref>{{cite journal|title=Modules for Standard ML, LFP '84 Proceedings of the 1984 ACM Symposium on LISP and functional programming|pages=198–207|author=David MacQueen|date=August 1984}}</ref> has one of the most complete module systems, including [[Standard ML#Module system|functors]] (parameterized modules) to map between modules.
▲In the 1980s and 1990s, modular programming was overshadowed by and often conflated with [[object-oriented programming]], particularly due to the popularity of C++ and Java. For example, the C family of languages had support for objects and classes in C++ (originally [[C with Classes]], 1980) and Objective-C (1983), only supporting modules 30 years or more later. Java (1995) supports modules in the form of packages, though the primary unit of code organization is a class. However, Python (1991) prominently used both modules and objects from the start, using modules as the primary unit of code organization and "packages" as a larger-scale unit; and [[Perl 5]] (1994) includes support for both modules and objects, with a vast array of modules being available from [[CPAN]] (1993).
▲Modular programming is now widespread, and found in virtually all major languages developed since the 1990s. The relative importance of modules varies between languages, and in class-based object-oriented languages there is still overlap and confusion with classes as a unit of organization and encapsulation, but these are both well-established as distinct concepts.
==See also==
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* {{Annotated link|Cross-cutting concern}}
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* {{Annotated link|Information hiding}}
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* {{Annotated link|Structured programming}}
==References==
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* [http://www.smcsystem.ru/ SMC Platform]
▲{{Programming paradigms navbox}}
{{Authority control}}
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