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Double Dollars in PHP

What does this print?

<?php
$first = "fur";
$last = "feather";
$$first = "yum yum ";
${"$first$last"} = "yikes";
print "$fur $furfeather";
?>

It prints "yum yum yikes".

In PHP, you can write a variable name within a variable name, and that's what I've done in this example.

The variable called "first" is set to contain the word "fur"
The variable who's name is in first - so that's the variable called fur - is set to "yum yum"

The variable called "last" is set to "feather"
The variable who's name is made up of the string in the variable first followed by the string in the varaible last - so that's the variable called furfeather - is set to "yikes".

This is a facility to be used sparingly - it's quite easy to write code that's unmaintainable using such structures, though they can be very useful at times for helping to generalise code.
(written 2005-11-02, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
H103 - PHP - Variables, Operators and Expressions
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  [4324] Learning to program - variables and constants - (2014-11-22)
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [3916] PHP variables - dynamically typed. What does that mean? - (2012-11-08)
  [3278] Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. - (2011-05-05)
  [2215] If nothing, make it nothing. - (2009-06-02)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)

H999 - Additional PHP Material
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  [3210] Catchable fatal error in PHP ... How to catch, and alternative solutions such as JSON - (2011-03-22)
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  [2684] Exception handling in PHP - (2010-03-18)
  [2073] Extra PHP Examples - (2009-03-09)
  [1623] PHP Techniques - a workshop - (2008-04-26)
  [1519] Flipping images on your web page - (2008-01-26)
  [1505] Script to present commonly used images - PHP - (2008-01-13)
  [1485] Copyright and theft of images, bandwidth and members. - (2007-12-26)
  [1451] More PHP sample and demonstration programs - (2007-12-01)
  [1391] Ordnance Survey Grid Reference to Latitude / Longitude - (2007-10-14)
  [1390] Converting from postal address to latitude / longitude - (2007-10-13)
  [1389] Controlling and labelling Google maps via PHP - (2007-10-13)
  [1270] PHP Standalone - keyboard to screen - (2007-07-18)
  [1194] Drawing hands on a clock face - PHP - (2007-05-19)
  [1104] Drawing dynamic graphs in PHP - (2007-03-09)
  [1053] Sorting people by name in PHP - (2007-01-26)
  [1020] Parallel processing in PHP - (2007-01-03)
  [1010] Dates, times, clickable diarys in PHP - (2006-12-28)
  [937] Display an image from a MySQL database in a web page via PHP - (2006-11-22)
  [917] Syntax checking in PHP - (2006-11-07)
  [839] Reporting on the 10 largest files or 10 top scores - (2006-08-20)
  [822] PHP - a team member leaves - (2006-08-04)
  [806] Check your user is human. Have him retype a word in a graphic - (2006-07-17)
  [789] Hot answers in PHP - (2006-07-02)
  [687] Presentation, Business and Persistence layers in Perl and PHP - (2006-04-17)
  [665] PHP Image viewing application - (2006-04-01)
  [603] PHP - setting sort order with an associative array - (2006-02-13)
  [563] Merging pictures using PHP and GD - (2006-01-13)
  [493] Running a Perl script within a PHP page - (2005-11-12)
  [468] Stand alone PHP programs - (2005-10-18)
  [372] Time calculation in PHP - (2005-07-08)
  [337] the array returned by preg_match_all - (2005-06-06)
  [322] More maps - (2005-05-23)
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  [239] What and why for the epoch - (2005-03-08)
  [54] PHP and natural sorting - (2004-09-19)


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