In PHP, there are four methods to use callback functions, namely: 1. Use named functions as callbacks, by passing the function name as a string to functions such as array_map; 2. Use anonymous functions (closures), which are suitable for situations where logic is simple and only used once; 3. Use object methods as callbacks, by passing an array containing object and method names; 4. Use static methods as callbacks, you can add strings of method names through array syntax or class names. Each method has its applicable scenarios, and it is necessary to ensure that the callback is accessible and its validity can be verified through is_callable().
In PHP, using a function as a callback is straightforward and pretty common, especially when working with functions like array_map , array_filter , or event-driven systems. You can pass a function as a parameter to another function, and it will be executed at the right time.
1. Using a Named Function as a Callback
This is the most basic way. You define a function separately and then pass its name as a string to another function that expects a callback.
function multiply_by_two($n) {
return $n * 2;
}
$numbers = [1, 2, 3, 4];
$result = array_map('multiply_by_two', $numbers); Here, array_map applies multiply_by_two to every element in $numbers .
Note: The function name is passed as a string 'multiply_by_two' .
2. Using Anonymous Functions (Closures)
Anonymous functions are often used as callbacks, especially when the logic is short and doesn't need a separate named function.
$numbers = [1, 2, 3, 4];
$result = array_map(function($n) {
return $n * 2;
}, $numbers);This is useful for small logic that's only used once. You can also assign the closure to a variable and pass that:
$callback = function($n) {
return $n * 2;
};
$result = array_map($callback, $numbers);3. Using Object Methods as Callbacks
If you're working in an object-oriented context, you can use a method of a class as a callback. You need to pass an array where the first element is the object and the second is the method name.
class Math {
public function square($n) {
return $n * $n;
}
}
$math = new Math();
$numbers = [1, 2, 3, 4];
$result = array_map([$math, 'square'], $numbers);This is especially handy when you want to keep your logic organized inside classes.
4. Using Static Methods as Callbacks
You can also use static methods as callbacks. The syntax is similar, but you reference the class directly.
class Helper {
public static function add_one($n) {
return $n 1;
}
}
$numbers = [1, 2, 3, 4];
$result = array_map(['Helper', 'add_one'], $numbers);Or in PHP 5.2.3 and later, you can use:
$result = array_map('Helper::add_one', $numbers);
Either way works, but the array syntax is preferred in newer code.
A few things to remember:
- Make sure the function or method is accessible (not private if using in another context).
- Always check if the callback is valid using
is_callable()if you're unsure. - Closures can also capture variables from the parent scope using
use().
Basically that's it. Callbacks are very practical in PHP and are also flexible in usage. Mastering these methods can basically deal with most scenarios.
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