For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.
Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!
I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Take the dog on a lead - do not carry her. Perl references.
Taking the dog out for a walk? It's much easier to use a lead than to carry the whole dog.
And ... in a similar vein ... when you're passing some data into a named block of code
(a.k.a. sub, subroutine, function, procedure, command, method, macro) when programming, it's much more efficient to pass in a pointeri
(a.k.a. an address or a reference)
When you pass in a pointer, you're saving yourself having to duplicate the data. That can be a serious saving if you're working with large or huge data sets. And you're also providing a powerful (but dangerous if misused) capability of altering the original data within the code that you've called.
On yesterday's Perl course
, I wrote a fresh example that compares copying a list into a Perl sub, and passing in the address. The difference is just a \ !
Copying into the sub:
Passing a reference into the sub:
Full source code of the demo [here]
, including the source of the subs which must (of course) be coded to accept the data type that's being passed to them.
Perl's references are also an excellent way of setting up collections of collections - a very flexible and space-saving alternative to the multidimensional arrays of other languages. New example of those - [here]
. (written 2011-09-17, updated 2013-01-01)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articlesP217 - Perl - More than Simple Lists and Hashes! 
Hash of lists in Perl - (2004-09-09) 
Course follow-ups - (2005-04-27) 
Autovivification - the magic appearance of variables in Perl - (2008-01-21) 
Perl references - $$var and \$var notations - (2009-06-15) 
Just pass a pointer - do not duplicate the data - (2010-06-30) 
Further more advanced Perl examples - (2010-07-19) 
Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12) 
Setting up a matrix of data (2D array) for processing in your program - (2010-10-21) 
Finding elements common to many lists / arrays - (2010-11-26) 
Adventure with references to lists and lists of references - (2010-12-26) 
Arrays of arrays - or 2D arrays. How to program tables. - (2011-01-02) 
From fish, loaves and apples to money, plastic cards and BACS (Perl references explained) - (2011-08-20) 
Not multidimentional arrays - but lists of lists. Much more flexible. Perl! - (2011-08-26) 
How to do multidimensional arrays (or rather lists and hashes) in Perl - (2012-01-14) 
Taking the lead, not the dog, for a walk. - (2012-10-28)
Some other Articles
Checking all the systems on a subnet, using Expect and TkNeedle in a haystack - finding the web server overloadAwk v PerlPerl and CGI - simple form, and monitoring script.Take the dog on a lead - do not carry her. Perl references.Getting more log information from the Apache http web serverA demonstration of how many Python facilities work togetherPressing ^C in a Python program. Also Progress Bar.Research is exciting. But should routine be automated?Python for loops - applying a temporary second name to the same object
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This is a page archived from The Horse's Mouth at
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