If you've writing or maintaining a program and you find yourself cutting and pasting a chunk of code, STOP and think again.

By duplicating a block of code, you're duplicating your maintainance task from that point onwards - any fixes applied to the original much be applied to the copy too. And that's going to be very inefficient in time as you duplicate the duplicate and end up with a whole shed load of copies. There IS a better way!

Take the code that you would be duplicating, and put it somewhere separate. Give it a name (i.e. make it a named block of code) and call it up by name from both its original location, and from the location that you would have put the copy into. All modern languages support named blocks of code in this way:
• In Perl, they're known as subs which is short for subroutines
• In many other languages, they're known as functions or methods or macros
• In Tcl, they're known as procs which is short for procedures

"But I want to make a couple of changes to the block of code that I was going to duplicate" you might say. That's NOT a problem. The bits that you would change in the duplicated code are the bits that you'll pass in to your sub / function / method / procedure as parameters, and if you also change the variable that the result is going to be put into, that's the immediate clue as to what you'll be returning.

Where you want to share a named block of code between several programs, you can do so too. That's done through commands / calls such as import (Python, Java), source (Tcl), require (Perl, PHP), use (Perl), from (Python) and include (PHP). In C and C++, functions work across programs in a slightly different way - rather than including the reference in the source, you'll bring in prototypes in the source and then the full code in your link loader. But that's a story for another day ...
(written 2006-06-23 07:13:33)

 C204 - C and C based languages - Functions, Macros and programs in multiple files
  [2575] Sharing variables between files of code in C - extern - (2010-01-14)
  [2570] Function Prototypes in C - (2010-01-11)
  [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)

H105 - PHP - Functions
  [2682] Adding extensions to PHP Open Source applications - callbacks - (2010-03-17)
  [2630] Static variables and ampersands in PHP - (2010-02-10)
  [2488] A variable number of arguments in a PHP function - (2009-11-02)
  [1784] Global - Tcl, PHP, Python - (2008-09-03)
  [1380] Static variables in PHP - (2007-10-05)
  [1357] Clean my plate, but keep my wine bottle. (PHP; Static) - (2007-09-18)
  [1267] is there a lookup function in php? - (2007-07-15)
  [1202] Returning multiple values from a function (Perl, PHP, Python) - (2007-05-24)
  [1021] PHP - static declaration - (2007-01-04)
  [936] Global, Superglobal, Session variables - scope and persistance in PHP - (2006-11-21)
  [866] A lazy programmer is a good programmer - (2006-09-15)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [409] Functions and commands with dangerous names - (2005-08-11)
  [340] Code and code maintainance efficiency - (2005-06-08)
  [339] Passing information into and out of PHP functions - (2005-06-07)
  [308] Call by name v call by value - (2005-05-11)
  [223] There is a function in PHP to do that - (2005-02-21)
  [96] Variable Scope - (2004-10-22)

P209 - Subroutines in Perl
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2069] Efficient calls to subs in Perl - avoid duplication, gain speed - (2009-03-07)
  [1921] Romeo and Julie - (2008-12-04)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1850] Daisy the Cow and a Pint of Ginger Beer - (2008-10-21)
  [1826] Perl - Subs, Chop v Chomp, => v , - (2008-10-08)
  [1782] Calling procs in Tcl and how it compares to Perl - (2008-09-02)
  [969] Perl - $_ and @_ - (2006-12-07)
  [588] Changing @INC - where Perl loads its modules - (2006-02-02)
  [531] Packages in packages in Perl - (2005-12-16)
  [357] Where do Perl modules load from - (2005-06-24)

T207 - Tcl/Tk - Procedures and Variable Scope
  [2520] Global and Enable - two misused words! - (2009-11-30)
  [2476] Tcl - uplevel to run code at calling level - (2009-10-24)
  [2466] Tcl - passing arrays and strings in and back out of procs - (2009-10-22)
  [1404] Tcl - global, upvar and uplevel. - (2007-10-24)
  [122] Passing arrays to procs in Tcl - (2004-11-18)

Y105 - Python - Functions, Modules and Packages
  [2506] Good example of recursion in Python - analyse an RSS feed - (2009-11-18)
  [2481] Sample code with errors in it on our web site - (2009-10-29)
  [2440] Optional parameters to Python functions - (2009-10-07)
  [2439] Multiple returns from a function in Python - (2009-10-06)
  [2011] Conversion of OSI grid references to Eastings and Northings - (2009-01-28)
  [1879] Dynamic code - Python - (2008-11-11)
  [1871] Optional and named parameters in Python - (2008-11-05)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1869] Anonymous functions (lambdas) and map in Python - (2008-11-04)
  [1790] Sharing variables with functions, but keeping them local too - Python - (2008-09-09)
  [1464] Python Script - easy examples of lots of basics - (2007-12-08)
  [1134] Function / method parameters with * and ** in Python - (2007-04-04)
  [959] It's the 1st, not the 1nd 1rd or 1th. - (2006-12-01)
  [949] Sludge off the mountain, and Python and PHP - (2006-11-27)
  [913] Python - A list of methods - (2006-11-03)
  [912] Recursion in Python - (2006-11-02)
  [900] Python - function v method - (2006-10-20)
  [821] Dynamic functions and names - Python - (2006-08-03)
  [749] Cottage industry or production line data handling methods - (2006-06-07)
  [745] Python modules. The distribution, The Cheese Shop and the Vaults of Parnassus. - (2006-06-05)
  [668] Python - block insets help with documentation - (2006-04-04)
  [561] Python's Generator functions - (2006-01-11)
  [418] Difference between import and from in Python - (2005-08-18)
  [386] What is a callback? - (2005-07-22)
  [303] Lambdas in Python - (2005-05-06)
  [294] Python generator functions, lambdas, and iterators - (2005-04-28)
  [105] Distance Learning - (2004-10-31)

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Do not duplicate your code
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