- Legacy code
Legacy code is
source code that relates to a no-longer supported or manufacturedoperating system or othercomputer technology. The term can also mean code inserted into modern software for the purpose of maintaining an older or previously supported feature — for example supporting a serial interface even though many modern systems don't have aserial port . It may also be in the form of supporting older file formats that may have been encoding in non-ASCII characters, such asEBCDIC .In practice, most source code has some dependency on the platform for which it is designed—unless a programmer uses a platform-independent programming language like Java, it is hard to write a large, useful program that is totally independent of its environment. When the manufacturer upgrades or supersedes the platform, the code will no longer work without changes, and becomes legacy code. A large part of the task of a
software engineer is to continually alter code to prevent this.While the term usually refers to source code, it can occasionally be heard applied to
executable code that no longer runs on a modern version of a system, or requires acompatibility layer to do so. An example would be a classic Macintosh application which will not run natively onMac OS X , but runs inside the Classic environment, or aWin16 application running onWindows XP using theWindows on Windows feature in XP.Modern interpretations
More recently, the
software engineering community has developed other interpretations for the term "legacy code". Among the most prevalent are "source code inherited from someone else" and "source code inherited from an older version of the software". Michael Feathers' "Working Effectively with Legacy Code" (ISBN 0-13-117705-2) introduced a definition of "legacy code" as "code without tests", which reflects the perspective of legacy code being difficult to work with in part due to a lack of automated regression tests. He also defined Characterization Tests to start putting "legacy code" under test.ee also
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Legacy system
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