PHP: Array Operators


This is a Comprehensive PHP array operators tutorial from w3resource.com

List of array operators

Name Example Result
Union $x + $y Union of $x and $y. The + operator appends elements of remaining keys from the right-sided array to the left-handed, but duplicated keys are not overwritten.
Equality $x == $y TRUE if $x and $y have the same key/value pairs.
Identity $x === $y TRUE if $x and $y have the same key/value pairs in the same order and of the same types.
Inequality $x != $y TRUE if $x is not equal to $y.
Inequality $x <> $y TRUE if $x is not equal to $y.
Non-identity $x !== $y TRUE if $x is not identical to $y.

Example : array union (+) operator

In the following example, the union operator adds the last element from the $b array ($c = $a + $b) with $a array as "c=>" key is not present in $a array. In the second statement ($c = $b + $a) no element is added from $b as all the keys of $a array are present in $b array.

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b : <br />";
$c = $b + $a; // Union of $b and $a 
echo "<br />Union of \$b and \$a : <br />";


Union of $a and $b: 
array(3) {    ["a"]=>    string(5) "apple"    ["b"]=>    string(6) "banana"    ["c"]=>    string(6) "cherry"  } 
Union of $b and $a :
array(3) {    ["a"]=>    string(4) "pear"    ["b"]=>    string(10) "strawberry"    ["c"]=>    string(6) "cherry"  } 

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Example : array equality (==) and identity(===) operators

In the following example equality operator returns true as the two arrays have same key/value pairs whereas identity operator returns false as the key/value of the comparing arrays are same but not in same order.

$a = array("1" => "apple", "0" => "banana");
$b = array( "banana", "apple");
var_dump($a == $b);
var_dump($a === $b);


bool(true)  bool(false) 

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Previous: String Operators
Next: Incrementing Decrementing Operators

PHP: Tips of the Day

PHP - How do I implement a callback in PHP?

The manual uses the terms "callback" and "callable" interchangeably, however, "callback" traditionally refers to a string or array value that acts like a function pointer, referencing a function or class method for future invocation. This has allowed some elements of functional programming since PHP 4. The flavors are:

$cb1 = 'someGlobalFunction';
$cb2 = ['ClassName', 'someStaticMethod'];
$cb3 = [$object, 'somePublicMethod'];

// this syntax is callable since PHP 5.2.3 but a string containing it
// cannot be called directly
$cb2 = 'ClassName::someStaticMethod';
$cb2(); // fatal error

// legacy syntax for PHP 4
$cb3 = array(&$object, 'somePublicMethod');

This is a safe way to use callable values in general:

if (is_callable($cb2)) {
    // Autoloading will be invoked to load the class "ClassName" if it's not
    // yet defined, and PHP will check that the class has a method
    // "someStaticMethod". Note that is_callable() will NOT verify that the
    // method can safely be executed in static context.

    $returnValue = call_user_func($cb2, $arg1, $arg2);

Modern PHP versions allow the first three formats above to be invoked directly as $cb(). call_user_func and call_user_func_array support all the above.


  1. If the function/class is namespaced, the string must contain the fully-qualified name. E.g. ['Vendor\Package\Foo', 'method']
  2. call_user_func does not support passing non-objects by reference, so you can either use call_user_func_array or, in later PHP versions, save the callback to a var and use the direct syntax: $cb();
  3. Objects with an __invoke() method (including anonymous functions) fall under the category "callable" and can be used the same way, but I personally don't associate these with the legacy "callback" term.
  4. The legacy create_function() creates a global function and returns its name. It's a wrapper for eval() and anonymous functions should be used instead.

Ref : https://bit.ly/2Zmqil0