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{{Short description|
'''Modular programming''' is a [[software
A module [[
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}}
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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 [[Assembly (CLI)|assembly]] (as in [[.NET
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 (programming language)|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.
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==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}}
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