ZEND PHP 5 Certification STUDY GUIDE

PHP Basics ” 21
$b = $a;
$b = 20;
echo $a; // Outputs 10
Naturally, you expect this to be the case, but there are circumstances in which you
may want an assignment to take place by reference, so that the left-hand operand
becomes “connected” with the right-hand one:
i
$a = 10;
$b = &$a; // by reference
$b = 20;
echo $a; // Outputs 20
The assignment operator works by value for all data types, except objects, which are
always passed by reference, regardless of whether the & operator is used or not.
The use of by-reference variables is a sometimes-useful, but always very risky technique,
because PHP variables tend to stay in scope for a long time, even within a
single function. Additionally, unlike what happens in many other languages, byreference
activity is often slower than its by-value counterpart, because PHP uses
a clever “deferred-copy” mechanism that actually optimizes by-value assignments.
Comparison Operators
Comparison operations are binary operations that establish a relationship of equivalence
between two values. They can either establish whether two values are equal
(or not equal) to each other, and whether one is greater (or smaller) than the other.
The result of a comparison operation is always a Boolean value.
There are four equivalence operations:
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)