The basic assignment operator is "=". Your first inclination might be to think of this as "equal to". Don't. It really means that the left operand gets set to the value of the expression on the right (that is, "gets set to").
The value of an assignment expression is the value assigned. That is, the value of "$a = 3" is 3. This allows you to do some tricky things:
Example #1 Nested Assignments
<?php
$a= ($b=4) +5;// $a is equal to 9 now, and $b has been set to 4.
var_dump($a);
?>In addition to the basic assignment operator, there are "combined operators" for all of thebinary arithmetic, array union and string operators that allow you to use a value in an expression and then set its value to the result of that expression. For example:
Example #2 Combined Assignments
<?php
$a=3;
$a+=5;// sets $a to 8, as if we had said: $a = $a + 5;
$b="Hello ";
$b.="There!";// sets $b to "Hello There!", just like $b = $b . "There!";
var_dump($a,$b);
?>Note that the assignment copies the original variable to the new one (assignment by value), so changes to one will not affect the other. This may also have relevance if you need to copy something like a large array inside a tight loop.
An exception to the usual assignment by value behaviour within PHP occurs withobjects, which are assigned by reference. Objects may be explicitly copied via theclone keyword.
Assignment by reference is also supported, using the "$var = &$othervar;" syntax. Assignment by reference means that both variables end up pointing at the same data, and nothing is copied anywhere.
Example #3 Assigning by reference
<?php
$a=3;
$b= &$a;// $b is a reference to $a
print"$a\n";// prints 3
print"$b\n";// prints 3
$a=4;// change $a
print"$a\n";// prints 4
print"$b\n";// prints 4 as well, since $b is a reference to $a, which has
// been changed
?>Thenew operator returns a reference automatically, as such assigning the result ofnew by reference is an error.
Example #4 new Operator By-Reference
<?php
classC{}
$o= &newC;
?>The above example will output:
Parse error: syntax error, unexpected token ";", expecting "("More information on references and their potential uses can be found in theReferences Explained section of the manual.
| Example | Equivalent | Operation |
|---|---|---|
| $a += $b | $a = $a + $b | Addition |
| $a -= $b | $a = $a - $b | Subtraction |
| $a *= $b | $a = $a * $b | Multiplication |
| $a /= $b | $a = $a / $b | Division |
| $a %= $b | $a = $a % $b | Modulus |
| $a **= $b | $a = $a ** $b | Exponentiation |
| Example | Equivalent | Operation |
|---|---|---|
| $a &= $b | $a = $a & $b | Bitwise And |
| $a |= $b | $a = $a | $b | Bitwise Or |
| $a ^= $b | $a = $a ^ $b | Bitwise Xor |
| $a <<= $b | $a = $a << $b | Left Shift |
| $a >>= $b | $a = $a >> $b | Right Shift |
| Example | Equivalent | Operation |
|---|---|---|
| $a .= $b | $a = $a . $b | String Concatenation |
| $a ??= $b | $a = $a ?? $b | Null Coalesce |
Using $text .= "additional text"; instead of $text = $text ."additional text"; can seriously enhance performance due to memory allocation efficiency. I reduced execution time from 5 sec to .5 sec (10 times) by simply switching to the first pattern for a loop with 900 iterations over a string $text that reaches 800K by the end.Be aware of assignments with conditionals. The assignment operator is stronger as 'and', 'or' and 'xor'.<?php $x=trueandfalse;//$x will be true$y= (trueandfalse);//$y will be false?>bradlis7 at bradlis7 dot com's description is a bit confusing. Here it is rephrased.<?php$a='a';$b='b';$a.=$b.="foo";echo$a,"\n",$b;?>outputsabfoobfooBecause the assignment operators are right-associative and evaluate to the result of the assignment<?php$a.=$b.="foo";?>is equivalent to<?php$a.= ($b.="foo");?>and therefore<?php$b.="foo";$a.=$b;?>PHP uses a temporary variable for combined assign-operators (unlike JavaScript), therefore the left-hand-side (target) gets evaluated last.Input:$a += $b + $c; Meaning:$a = ($b + $c) + $a;Not:$a = $a + ($b + $c);This can be important if the target gets modified inside the expression.$a = 0;$a += (++$a) + (++$a); // yields 5 (instead of 4)