 | This article has multiple issues. Please helpimprove it or discuss these issues on thetalk page.(Learn how and when to remove these messages) (Learn how and when to remove this message)
|
Metaprogramming is acomputer programming technique in whichcomputer programs have the ability to treat other programs as theirdata. It means that a program can be designed to read, generate, analyse, or transform other programs, and even modify itself, while running.[1][2] In some cases, this allows programmers to minimize the number of lines of code to express a solution, in turn reducing development time.[3] It also allows programs more flexibility to efficiently handle new situations with no recompiling.
Metaprogramming can be used to move computations fromruntime tocompile time, to generate code usingcompile time computations, and to enableself-modifying code. The ability of aprogramming language to be its ownmetalanguage allowsreflective programming, and is termedreflection.[4] Reflection is a valuable language feature to facilitate metaprogramming.
Metaprogramming was popular in the 1970s and 1980s using list processing languages such asLisp.Lisp machine hardware gained some notice in the 1980s, and enabled applications that could process code. They were often used forartificial intelligence applications.
Metaprogramming enables developers to write programs and develop code that falls under thegeneric programmingparadigm. Having the programming language itself as afirst-class data type (as inLisp,Prolog,SNOBOL, orRebol) is also very useful; this is known ashomoiconicity.Generic programming invokes a metaprogramming facility within a language by allowing one to write code without the concern of specifying data types since they can be supplied asparameters when used.
Metaprogramming usually works in one of three ways.[5]
Lisp is probably the quintessential language with metaprogramming facilities, both because of its historical precedence and because of the simplicity and power of its metaprogramming. In Lisp metaprogramming, the unquote operator (typically a comma) introduces code that isevaluated at program definition time rather than at run time. The metaprogramming language is thus identical to the host programming language, and existing Lisp routines can be directly reused for metaprogramming if desired. This approach has been implemented in other languages by incorporating an interpreter in the program, which works directly with the program's data. There are implementations of this kind for some common high-level languages, such asRemObjects’Pascal Script forObject Pascal.
A simple example of a metaprogram is thisPOSIX Shellscript, which is an example ofgenerative programming:
#!/bin/sh# metaprogramecho'#!/bin/sh'>programforiin$(seq992)doecho"echo$i">>programdonechmod+xprogram
This script (or program) generates a new 993-line program that prints out the numbers 1–992. This is only an illustration of how to use code to write more code; it is not the most efficient way to print out a list of numbers. Nonetheless, a programmer can write and execute this metaprogram in less than a minute, and will have generated over 1000 lines of code in that amount of time.
Aquine is a special kind of metaprogram that produces its own source code as its output. Quines are generally of recreational or theoretical interest only.
Not all metaprogramming involves generative programming. If programs are modifiable at runtime, or if incremental compiling is available (such as inC#,Forth,Frink,Groovy,JavaScript,Lisp,Elixir,Lua,Nim,Perl,PHP,Python,Rebol,Ruby,Rust,R,SAS,Smalltalk, andTcl), then techniques can be used to perform metaprogramming without generating source code.
One style of generative approach is to employdomain-specific languages (DSLs). A fairly common example of using DSLs involves generative metaprogramming:lex andyacc, two tools used to generatelexical analysers andparsers, let the user describe the language usingregular expressions andcontext-free grammars, and embed the complex algorithms required to efficiently parse the language.
One usage of metaprogramming is to instrument programs in order to dodynamic program analysis.
Some argue that there is a sharp learning curve to make complete use of metaprogramming features.[8] Since metaprogramming gives more flexibility and configurability at runtime, misuse or incorrect use of metaprogramming can result in unwarranted and unexpected errors that can be extremely difficult to debug to an average developer. It can introduce risks in the system and make it more vulnerable if not used with care. Some of the common problems, which can occur due to wrong use of metaprogramming are inability of the compiler to identify missing configuration parameters, invalid or incorrect data can result in unknown exception or different results.[9] Due to this, some believe[8] that only high-skilled developers should work on developing features which exercise metaprogramming in a language or platform and average developers must learn how to use these features as part of convention.
TheIBM/360 and derivatives had powerfulmacro assembler facilities that were often used to generate completeassembly language programs[citation needed] or sections of programs (for different operating systems for instance). Macros provided withCICStransaction processing system had assembler macros that generatedCOBOL statements as a pre-processing step.
Other assemblers, such asMASM, also support macros.
Metaclasses are provided by the following programming languages:
Use ofdependent types allows proving that generated code is never invalid.[15] However, this approach is leading-edge and rarely found outside of research programming languages.
The list of notable metaprogramming systems is maintained atList of program transformation systems.
 | This article mayrequirecleanup to meet Wikipedia'squality standards. The specific problem is:archive-org link links to unrelated maybe-spam site, unclear if legitimate bit rot or malice. Please helpimprove this article if you can.(April 2025) (Learn how and when to remove this message) |
