İfadeler
Method chaining is read left to right (left associative):
<?php
class Test_Method_Chain
{
public function One()
{
echo "One" . PHP_EOL;
return $this;
}
public function Two()
{
echo "Two" . PHP_EOL;
return $this;
}
public function Three()
{
echo "Three" . PHP_EOL;
return $this;
}
}
$test = new Test_Method_Chain();
$test->One()->Two()->Three();
/* Ouputs:
One
Two
Three
*/
?>
Bölüm 10. Operators
An operator is something that you feed with one or more values (or expressions, in programming jargon) which yields another value (so that the construction itself becomes an expression). So you can think of functions or constructions that return a value (like print) as operators and those that return nothing (like echo) as any other thing.
There are three types of operators. Firstly there is the unary operator which operates on only one value, for example ! (the negation operator) or ++ (the increment operator). The second group are termed binary operators; this group contains most of the operators that PHP supports, and a list follows below in the section Operator Precedence.
The third group is the ternary operator: ?:. It should be used to select between two expressions depending on a third one, rather than to select two sentences or paths of execution. Surrounding ternary expressions with parentheses is a very good idea.
Operator Precedence
The precedence of an operator specifies how "tightly" it binds two expressions together. For example, in the expression 1 + 5 * 3, the answer is 16 and not 18 because the multiplication ("*") operator has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18. If operator precedence is equal, left to right associativity is used.
The following table lists the precedence of operators with the highest-precedence operators listed at the top of the table. Operators on the same line have equal precedence, in which case their associativity decides which order to evaluate them in.
Tablo 10-1. Operator Precedence
| Associativity | Operators |
|---|---|
| non-associative | new |
| right | [ |
| right | ! ~ ++ -- (int) (float) (string) (array) (object) @ |
| left | * / % |
| left | + - . |
| left | << >> |
| non-associative | < <= > >= |
| non-associative | == != === !== |
| left | & |
| left | ^ |
| left | | |
| left | && |
| left | || |
| left | ? : |
| right | = += -= *= /= .= %= &= |= ^= <<= >>= |
| right | |
| left | and |
| left | xor |
| left | or |
| left | , |
Not: Although ! has a higher precedence than =, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the output from foo() is put into $a.
add a note
User Contributed Notes
Operators
pgarvin76+php dot net at NOSPAMgmail dot com
29-Dec-2008 04:43
ddascalescu at gmail dot com
23-Oct-2008 06:53
The -> operator, not listed above, is called "object operator" (T_OBJECT_OPERATOR).
figroc at gmail dot com
02-Aug-2008 03:30
The variable symbol '$' should be considered as the highest-precedence operator, so that the variable variables such as $$a[0] won't confuse the parser. [http://www.php.net/manual/en/language.variables.variable.php]
phpnet dot 20 dot dpnsubs at xoxy dot net
01-Nov-2007 02:13
Note that in php the ternary operator ?: has a left associativity unlike in C and C++ where it has right associativity.
You cannot write code like this (as you may have accustomed to in C/C++):
<?php
$a = 2;
echo (
$a == 1 ? 'one' :
$a == 2 ? 'two' :
$a == 3 ? 'three' :
$a == 4 ? 'four' : 'other');
echo "\n";
// prints 'four'
?>
You need to add brackets to get the results you want:
<?
$a = 2;
echo ($a == 1 ? 'one' :
($a == 2 ? 'two' :
($a == 3 ? 'three' :
($a == 4 ? 'four' : 'other') ) ) );
echo "\n";
//prints 'two'
?>
Gautam
10-Oct-2007 03:22
<?php
$result1 = 7 + 8 * 9/3 -4;
$result2 = 7 + 8 * (9/3 -4);
$result3 =(7 + 8)* 9/3 -4;
echo "Result1 for 7 + 8 * 9/3 -4 = $result1 Result2 for 7 + 8 * (9/3 -4) = $result2 and Result3 (7 + 8)* 9/3 -4 = $result3 "
/*
which gives results as under
Result1 for 7 + 8 * 9/3 -4 = 27 Result2 for 7 + 8 * (9/3 -4) = -1 and Result3 (7 + 8)* 9/3 -4 = 41
Execution Order is 1) expression in brackets 2) division 3) multiplication 4) addition and 5) subtraction
*/
?>
janturon at email dot cz
08-Oct-2007 06:42
This is very common problem: set one variable to another, if it is not empty. If it is, set it to something else.
For example: set $bar to $foo, if $foo is empty, set $bar to "undefined";
if(!empty($foo)) $bar= $foo; else $bar= "undefined";
OR operator can shorten it:
$bar= @$foo or $bar= "undefined";
me at robrosenbaum dot com
12-Jul-2007 12:16
The scope resolution operator ::, which is missing from the list above, has higher precedence than [], and lower precedence than 'new'. This means that self::$array[$var] works as expected.
madcoder at gmail dot com
09-Jun-2007 03:17
In response to mathiasrav at gmail dot com:
The reason for that behavior is the parentheses. From the description:
"Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18."
So the order of operations says that even though the equality operator has higher precedence, the parentheses in your statement force the assignment operator to a higher precedence than the equality operator.
That said, it still doesn't work the way you expect it to. Neither way works, for these reasons:
<?php
if ( $a != ($a = $b) )
?>
Order of operations says to do the parentheses first. So you end up with:
<?php
$a = $b;
if ( $a != $a )
?>
Which is obviously going to be false. Without the parentheses:
<?php
if ( $a != $a = $b )
?>
Order of operations says to do the inequality first, then the assignment, so you have:
<?php
if ( $a != $a );
$a = $b;
?>
Which again is not what you expected, and again will always be false. But because you are only working with values of 0 and 1, you can make use of the XOR operator:
<?php
if ( $a ^= $b )
?>
This will only be true if 1) $a is 0 and $b is 1, or 2) $a is 1 and $b is 0. That is precisely what you wanted, and it even does the assignment the way you expected it to.
<?php
foreach ($ourstring as $c) {
if ($bold ^= $c['bold']) $resstring .= bold;
if ($underline ^= $c['underline']) $resstring .= underline;
$resstring .= $c[0];
}
?>
That code now works and produces the output you expected.
golotyuk at gmail dot com
09-Jul-2006 09:51
Simple POST and PRE incremnt sample:
<?php
$b = 5;
$a = ( ( ++$b ) > 5 ); // Pre-increment test
echo (int)$a;
$b = 5;
$a = ( ( $b++ ) > 5 ); // Post-increment test
echo (int)$a;
?>
This will output 10, because of the difference in post- and pre-increment operations
rick at nomorespam dot fourfront dot ltd dot uk
02-Sep-2005 03:51
A quick note to any C developers out there, assignment expressions are not interpreted as you may expect - take the following code ;-
<?php
$a=array(1,2,3);
$b=array(4,5,6);
$c=1;
$a[$c++]=$b[$c++];
print_r( $a ) ;
?>
This will output;-
Array ( [0] => 1 [1] => 6 [2] => 3 )
as if the code said;-
$a[1]=$b[2];
Under a C compiler the result is;-
Array ( [0] => 1 [1] => 5 [2] => 3 )
as if the code said;-
$a[1]=$b[1];
It would appear that in php the increment in the left side of the assignment is processed prior to processing the right side of the assignment, whereas in C, neither increment occurs until after the assignment.
09-Jun-2004 05:58
of course this should be clear, but i think it has to be mentioned espacially:
AND is not the same like &&
for example:
<?php $a && $b || $c; ?>
is not the same like
<?php $a AND $b || $c; ?>
the first thing is
(a and b) or c
the second
a and (b or c)
'cause || has got a higher priority than and, but less than &&
of course, using always [ && and || ] or [ AND and OR ] would be okay, but than you should at least respect the following:
<?php $a = $b && $c; ?>
<?php $a = $b AND $c; ?>
the first code will set $a to the result of the comparison $b with $c, both have to be true, while the second code line will set $a like $b and THAN - after that - compare the success of this with the value of $c
maybe usefull for some tricky coding and helpfull to prevent bugs :D
greetz, Warhog
yasuo_ohgaki at hotmail dot com
25-Mar-2001 11:53
Other Language books' operator precedence section usually include "(" and ")" - with exception of a Perl book that I have. (In PHP "{" and "}" should also be considered also). However, PHP Manual is not listed "(" and ")" in precedence list. It looks like "(" and ")" has higher precedence as it should be.
Note: If you write following code, you would need "()" to get expected value.
<?php
$bar = true;
$str = "TEST". ($bar ? 'true' : 'false') ."TEST";
?>
Without "(" and ")" you will get only "true" in $str.
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It's due to precedence, probably.