This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.
It used to be hard to find questions about operators and other syntax tokens.¹
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the PHP Manual.
Note: Since January 2013, Stack Overflow does support special characters. Just surround the search terms by quotes, e.g. [php] "==" vs "==="
If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute to the help others provided.
If your particular token is not listed below, you might find it in the List of Parser Tokens.
& Bitwise Operators or References
=& References
?? Null Coalesce Operator (since PHP 7)
?string
?int
?array
?bool
?float Nullable return type declaration (since PHP 7.1)
: Alternative syntax for control structures, Ternary Operator
=> Arrays
<=> Comparison Operators (since PHP 7.0)
+ Arithmetic Operators, Array Operators
+= and -= Assignment Operators
++ and -- Incrementing/Decrementing Operators
<?= Short Open Tags
[] Arrays (short syntax since PHP 5.4)
$var = [] empty array... Argument unpacking (since PHP 5.6)
** Exponentiation (since PHP 5.6)
# One-line shell-style comment
?-> NullSafe Operator Calls (since PHP 8.0)
PHP 7 adds support for return type declarations. Similarly to argument type declarations, return type declarations specify the type of value that will be returned from a function. The same types are available for return type declarations as are available for argument type declarations.
Strict typing also has an effect on return type declarations. In the default weak mode, returned values will be coerced to the correct type if they are not already of that type. In strong mode, the returned value must be of the correct type, otherwise, a TypeError will be thrown.
As of PHP 7.1.0, return values can be marked as nullable by prefixing the type name with a question mark (?). This signifies that the function returns either the specified type or NULL.
<?php
function get_item(): ?string {
if (isset($_GET['item'])) {
return $_GET['item'];
} else {
return null;
}
}
?>
What is a bit? A bit is a representation of 1 or 0. Basically OFF(0) and ON(1)
What is a byte? A byte is made up of 8 bits and the highest value of a byte is 255, which would mean every bit is set. We will look at why a byte's maximum value is 255.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
This representation of 1 Byte
1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 (1 Byte)
&$a = 9;
$b = 10;
echo $a & $b;
This would output the number 8. Why? Well let's see using our table example.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| & | 0| 0| 0| 0| 1| 0| 0| 0|
-------------------------------------------
So you can see from the table the only bit they share together is the 8 bit.
Second example
$a = 36;
$b = 103;
echo $a & $b; // This would output the number 36.
$a = 00100100
$b = 01100111
The two shared bits are 32 and 4, which when added together return 36.
|$a = 9;
$b = 10;
echo $a | $b;
This would output the number 11. Why?
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| | | 0| 0| 0| 0| 1| 0| 1| 1|
-------------------------------------------
You will notice that we have 3 bits set, in the 8, 2, and 1 columns. Add those up: 8+2+1=11.
PHP Strings: PHP Strings can be specified in four ways not just two ways:
1) Single Quote Strings:
$string = 'This is my string'; // print This is my string
2) Double Quote Strings:
$str = 'string';
$string = "This is my $str"; // print This is my string
3) Heredoc:
$string = <<<EOD
This is my string
EOD; // print This is my string
4) Nowdoc (since PHP 5.3.0):
$string = <<<'END_OF_STRING'
This is my string
END_OF_STRING; // print This is my string
Question:
What does "&" mean here in PHP?
Makes life more easier once we get used to it..(check example below carefully)
& usually checks bits that are set in both $a and $b are set.
have you even noticed how these calls works?
error_reporting(E_ERROR | E_WARNING | E_PARSE);
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
error_reporting(E_ALL & ~E_NOTICE);
error_reporting(E_ALL);
So behind all above is game of bitwise operator and bits.
One usefull case of these is easy configurations like give below, so a single integer field can store thousands of combos for you.
Most people have already read the docs but didn't reliase the real world use case of these bitwise operators.
<?php
class Config {
// our constants must be 1,2,4,8,16,32,64 ....so on
const TYPE_CAT=1;
const TYPE_DOG=2;
const TYPE_LION=4;
const TYPE_RAT=8;
const TYPE_BIRD=16;
const TYPE_ALL=31;
private $config;
public function __construct($config){
$this->config=$config;
if($this->is(Config::TYPE_CAT)){
echo 'cat ';
}
if($this->is(Config::TYPE_DOG)){
echo 'dog ';
}
if($this->is(Config::TYPE_RAT)){
echo 'rat ';
}
if($this->is(Config::TYPE_LION)){
echo 'lion ';
}
if($this->is(Config::TYPE_BIRD)){
echo 'bird ';
}
echo "\n";
}
private function is($value){
return $this->config & $value;
}
}
new Config(Config::TYPE_ALL);
// cat dog rat lion bird
new Config(Config::TYPE_BIRD);
//bird
new Config(Config::TYPE_BIRD | Config::TYPE_DOG);
//dog bird
new Config(Config::TYPE_ALL & ~Config::TYPE_DOG & ~Config::TYPE_CAT);
//rat lion bird
Added in PHP 8.0
It's the NullSafe Operator, it returns null in case you try to invoke functions or get values from null. Nullsafe operator can be chained and can be used both on the methods and properties.
$objDrive = null;
$drive = $objDrive?->func?->getDriver()?->value; //return null
$drive = $objDrive->func->getDriver()->value; // Error: Trying to get property 'func' of non-object
Nullsafe operator doesn't work with array keys:
$drive['admin']?->getDriver()?->value //Warning: Trying to access array offset on value of type null
$drive = [];
$drive['admin']?->getAddress()?->value //Warning: Undefined array key "admin"
Magic constants: Although these are not just symbols but important part of this token family. There are eight magical constants that change depending on where they are used.
__LINE__: The current line number of the file.
__FILE__: The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.
__DIR__: The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)
__FUNCTION__: The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__CLASS__: The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased. The class name includes the namespace it was declared in (e.g. Foo\Bar). Note that as of PHP 5.4 __CLASS__ works also in traits. When used in a trait method, __CLASS__ is the name of the class the trait is used in.
__TRAIT__: The trait name. (Added in PHP 5.4.0) As of PHP 5.4 this constant returns the trait as it was declared (case-sensitive). The trait name includes the namespace it was declared in (e.g. Foo\Bar).
__METHOD__: The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).
__NAMESPACE__: The name of the current namespace (case-sensitive). This constant is defined in compile-time (Added in PHP 5.3.0).
QUESTION:
What does => mean?
ANSWER:
=> Is the symbol we humans decided to use to separate "Key" => "Value" pairs in Associative Arrays.
ELABORATING:
To understand this, we have to know what Associative Arrays are. The first thing that comes up when a conventional programmer thinks of an array (in PHP) would be something similar to:
$myArray1 = array(2016, "hello", 33);//option 1
$myArray2 = [2016, "hello", 33];//option 2
$myArray3 = [];//option 3
$myArray3[] = 2016;
$myArray3[] = "hello";
$myArray3[] = 33;
Where as, if we wanted to call the array in some later part of the code, we could do:
echo $myArray1[1];// output: hello
echo $myArray2[1];// output: hello
echo $myArray3[1];// output: hello
So far so good. However, as humans, we might find it hard to remember that index [0] of the array is the value of the year 2016, index [1] of the array is a greetings, and index [2] of the array is a simple integer value. The alternative we would then have is to use what is called an Associative Array. An Associative array has a few differences from a Sequential Array
(which is what the previous cases were since they increment the index used in a predetermined sequence, by incrementing by 1 for each following value).
Differences (between a sequential and associative array):
Durring the declaration of an Associative Array, you don't only include the value of what you want to put in the array, but you also put the index value (called the key) which you want to use when calling the array in later parts of the code. The following syntax is used during it's declaration: "key" => "value".
When using the Associative Array, the key value would then be placed inside the index of the array to retrieve the desired value.
For instance:
$myArray1 = array(
"Year" => 2016,
"Greetings" => "hello",
"Integer_value" => 33);//option 1
$myArray2 = [
"Year" => 2016,
"Greetings" => "hello",
"Integer_value" => 33];//option 2
$myArray3 = [];//option 3
$myArray3["Year"] = 2016;
$myArray3["Greetings"] = "hello";
$myArray3["Integer_value"] = 33;
And now, to receive the same output as before, the key value would be used in the arrays index:
echo $myArray1["Greetings"];// output: hello
echo $myArray2["Greetings"];// output: hello
echo $myArray3["Greetings"];// output: hello
FINAL POINT:
So from the above example, it is pretty easy to see that the => symbol is used to express the relationship of an Associative Array between each of the key and value pairs in an array DURING the initiation of the values within the array.
{} Curly braces
And some words about last post
$x[4] = 'd'; // it works
$x{4} = 'd'; // it works
$echo $x[4]; // it works
$echo $x{4}; // it works
$x[] = 'e'; // it works
$x{} = 'e'; // does not work
$x = [1, 2]; // it works
$x = {1, 2}; // does not work
echo "${x[4]}"; // it works
echo "${x{4}}"; // does not work
echo "{$x[4]}"; // it works
echo "{$x{4}}"; // it works
Not the catchiest name for an operator, but PHP 7 brings in the rather handy null coalesce so I thought I'd share an example.
In PHP 5, we already have a ternary operator, which tests a value, and then returns the second element if that returns true and the third if it doesn't:
echo $count ? $count : 10; // outputs 10
There is also a shorthand for that which allows you to skip the second element if it's the same as the first one: echo $count ?: 10; // also outputs 10
In PHP 7 we additionally get the ?? operator which rather than indicating extreme confusion which is how I would usually use two question marks together instead allows us to chain together a string of values. Reading from left to right, the first value which exists and is not null is the value that will be returned.
// $a is not set
$b = 16;
echo $a ?? 2; // outputs 2
echo $a ?? $b ?? 7; // outputs 16
This construct is useful for giving priority to one or more values coming perhaps from user input or existing configuration, and safely falling back on a given default if that configuration is missing. It's kind of a small feature but it's one that I know I'll be using as soon as my applications upgrade to PHP 7.
<=> (Added in PHP 7)Examples for <=> Spaceship operator (PHP 7, Source: PHP Manual):
Integers, Floats, Strings, Arrays & objects for Three-way comparison of variables.
// Integers
echo 10 <=> 10; // 0
echo 10 <=> 20; // -1
echo 20 <=> 10; // 1
// Floats
echo 1.5 <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1
// Strings
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1
// Comparison is case-sensitive
echo "B" <=> "a"; // -1
echo "a" <=> "aa"; // -1
echo "zz" <=> "aa"; // 1
// Arrays
echo [] <=> []; // 0
echo [1, 2, 3] <=> [1, 2, 3]; // 0
echo [1, 2, 3] <=> []; // 1
echo [1, 2, 3] <=> [1, 2, 1]; // 1
echo [1, 2, 3] <=> [1, 2, 4]; // -1
// Objects
$a = (object) ["a" => "b"];
$b = (object) ["a" => "b"];
echo $a <=> $b; // 0
$a = (object) ["a" => "b"];
$b = (object) ["a" => "c"];
echo $a <=> $b; // -1
$a = (object) ["a" => "c"];
$b = (object) ["a" => "b"];
echo $a <=> $b; // 1
// only values are compared
$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo $a <=> $b; // 1
| Syntax | Name | Description |
|---|---|---|
x == y |
Equality | true if x and y have the same key/value pairs |
x != y |
Inequality | true if x is not equal to y |
x === y |
Identity | true if x and y have the same key/value pairsin the same order and of the same types |
x !== y |
Non-identity | true if x is not identical to y |
++x |
Pre-increment | Increments x by one, then returns x |
x++ |
Post-increment | Returns x, then increments x by one |
--x |
Pre-decrement | Decrements x by one, then returns x |
x-- |
Post-decrement | Returns x, then decrements x by one |
x and y |
And | true if both x and y are true. If x=6, y=3 then(x < 10 and y > 1) returns true |
x && y |
And | true if both x and y are true. If x=6, y=3 then(x < 10 && y > 1) returns true |
x or y |
Or | true if any of x or y are true. If x=6, y=3 then(x < 10 or y > 10) returns true |
x || y |
Or | true if any of x or y are true. If x=6, y=3 then(x < 3 || y > 1) returns true |
a . b |
Concatenation | Concatenate two strings: "Hi" . "Ha" |
<=> Spaceship OperatorThe spaceship operator <=> is the latest comparison operator added in PHP 7. It is a non-associative binary operator with the same precedence as equality operators (==, !=, ===, !==). This operator allows for simpler three-way comparison between left-hand and right-hand operands.
The operator results in an integer expression of:
0 when both operands are equal0 when the left-hand operand is less than the right-hand operand0 when the left-hand operand is greater than the right-hand operande.g.
1 <=> 1; // 0
1 <=> 2; // -1
2 <=> 1; // 1
A good practical application of using this operator would be in comparison type callbacks that are expected to return a zero, negative, or positive integer based on a three-way comparison between two values. The comparison function passed to usort is one such example.
$arr = [4,2,1,3];
usort($arr, function ($a, $b) {
if ($a < $b) {
return -1;
} elseif ($a > $b) {
return 1;
} else {
return 0;
}
});
$arr = [4,2,1,3];
usort($arr, function ($a, $b) {
return $a <=> $b;
});
PHP has an operator "..." (Three dots) which is referred as Splat Operator. It is used to pass arbitrary number of parameters in a function and this type of function is called Variadic Functions. Let’s take examples to use of "..." (Three dots).
Example 1:
<?php
function calculateNumbers(...$params){
$total = 0;
foreach($params as $v){
$total = $total + $v;
}
return $total;
}
echo calculateNumbers(10, 20, 30, 40, 50);
//Output 150
?>
Each arguments of calculateNumbers() function pass through $params as an array when use "… ".
There are many different ways to use "… " operator. Below some examples:
Example 2:
<?php
function calculateNumbers($no1, $no2, $no3, $no4, $no5){
$total = $no1 + $no2 + $no3 + $no4 + $no5;
return $total;
}
$numbers = array(10, 20, 30, 40, 50);
echo calculateNumbers(...$numbers);
//Output 150
?>
Example 3:
<?php
function calculateNumbers(...$params){
$total = 0;
foreach($params as $v){
$total = $total + $v;
}
return $total;
}
$no1 = 70;
$numbers = array(10, 20, 30, 40, 50);
echo calculateNumbers($no1, ...$numbers);
//Output 220
?>
Example 4:
<?php
function calculateNumbers(...$params){
$total = 0;
foreach($params as $v){
$total = $total + $v;
}
return $total;
}
$numbers1 = array(10, 20, 30, 40, 50);
$numbers2 = array(100, 200, 300, 400, 500);
echo calculateNumbers(...$numbers1, ...$numbers2);
//Output 1650
?>
Null coalescing operator (??)
This operator has been added in PHP 7.0 for the common case of needing to use a ternary operator in conjunction with isset(). It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.
<?php
// Fetches the value of $_GET['user'] and returns 'nobody'
// if it does not exist.
$username = $_GET['user'] ?? 'nobody';
// This is equivalent to:
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';
// Coalescing can be chained: this will return the first
// defined value out of $_GET['user'], $_POST['user'], and
// 'nobody'.
$username = $_GET['user'] ?? $_POST['user'] ?? 'nobody';
?>
instanceof is used to determine whether a PHP variable is an instantiated object of a certain class.
<?php
class mclass { }
class sclass { }
$a = new mclass;
var_dump($a instanceof mclass);
var_dump($a instanceof sclass);
The above example will output:
bool(true)
bool(false)
Reason: Above Example $a is a object of the mclass so use only a mclass data not instance of with the sclass
<?php
class pclass { }
class childclass extends pclass { }
$a = new childclass;
var_dump($a instanceof childclass);
var_dump($a instanceof pclass);
The above example will output:
bool(true)
bool(true)
<?php
class cloneable { }
$a = new cloneable;
$b = clone $a;
var_dump($a instanceof cloneable);
var_dump($b instanceof cloneable);
The above example will output:
bool(true)
bool(true)
== is used for check equality without considering variable data-type
=== is used for check equality for both the variable value and data-type
$a = 5
if ($a == 5) - will evaluate to true
if ($a == '5') - will evaluate to true, because while comparing this both value PHP internally convert that string value into integer and then compare both values
if ($a === 5) - will evaluate to true
if ($a === '5') - will evaluate to false, because value is 5, but this value 5 is not an integer.
The underscore character '_' as in _() is an alias to the gettext() function.
and operator and or operator have lower precedence than assignment operator =.
This means that $a = true and false; is equivalent to ($a = true) and false.
In most cases you will probably want to use && and ||, which behave in a way known from languages like C, Java or JavaScript.
In PHP8 it's been accepted this new operator, you can find the documentation here. ?-> it's the NullSafe Operator, it returns null in case you try to invoke functions or get values from null...
Examples:
<?php
$obj = null;
$obj = $obj?->attr; //return null
$obj = ?->funct(); // return null
$obj = $objDrive->attr; // Error: Trying to get property 'attr' of non-object
?>
Source: Stackoverflow.com