Anonymous Functions

Anonymous functions (also known as closures) in PHP are functions that have no specified name. They are often used as callback functions or for cases where a function is only needed temporarily. Here’s a detailed overview of how they work:

Basic Syntax

$variable = function ($parameters) {
    // Code to execute
    return $value;
};

Example:

$greet = function($name) {
    return "Hello, " . $name;
};

echo $greet("John");  // Outputs: Hello, John

Anonymous Functions as Callbacks

They can also be passed to functions as arguments:

function processArray($array, $callback) {
    foreach ($array as $value) {
        echo $callback($value) . "\n";
    }
}

processArray([1, 2, 3], function($n) {
    return $n * 2;
});
// Outputs:
// 2
// 4
// 6

Use of use Keyword

Anonymous functions can “import” variables from the parent scope using the use keyword.

$message = "Hello";

$example = function($name) use ($message) {
    return $message . ", " . $name;
};

echo $example("Jane");  // Outputs: Hello, Jane

Anonymous Functions and Closures with Arguments by Reference

You can also pass variables by reference to modify them:

$counter = 0;

$increment = function() use (&$counter) {
    $counter++;
};

$increment();
$increment();

echo $counter;  // Outputs: 2

Conclusion

Anonymous functions are powerful when you need to define a function on the fly, such as in callbacks, short-lived operations, or encapsulating functionality that doesn’t need to be reused elsewhere. They can also capture variables from their surrounding scope using use.