


How do anonymous functions (closures) work in PHP, and what is the purpose of the use keyword with them?
Jun 09, 2025 am 12:14 AMAnonymous functions (closures) are functions without names in PHP and are often used in scenarios where callback functions need to be temporarily defined. They can be assigned to variables or passed directly as parameters, and are commonly used in array operations and event processing such as array_map and array_filter. Use the use keyword to allow the closure to inherit variables in the parent scope and pass by value by default. If you need to modify external variables, you should use the & symbol to pass by reference. Common application scenarios include: 1. Array processing; 2. Event registration; 3. Maintaining state callbacks; 4. Custom sorting logic. Closures help keep the code concise, but you need to pay attention to the scope and delivery of variables.
Anonymous functions, often called closings in PHP, are functions without a name. They're super handy when you need a quick function for a specific task and don't want to define a full named function. You'll often see them used as callbacks, especially in array functions like array_map
or array_filter
, or when working with objects that require callback handlers.
What Exactly Is an Anonymous Function?
An anonymous function is just like a regular function, but it doesn't have a name. You can assign it to a variable or pass it directly as an argument. Here's a basic example:
$greet = function($name) { echo "Hello, $name!"; }; $greet("John"); // Outputs: Hello, John!
In this case, the function is stored in the $greet
variable and then called like a regular function. This pattern is common in PHP when you only need a function once or when creating closings that capture external variables.
Why Use the use
Keyword?
When you define an anonymous function, it doesn't automatically have access to variables from the parent scope. That's where the use
keyword comes in. It allows the closure to inherit variables from the surrounding code.
Here's how it works:
$name = "Alice"; $greet = function() use ($name) { echo "Hello, $name"; }; $greet(); // Outputs: Hello, Alice
Without use
, the function wouldn't know what $name
is.
A few important things to note:
- Variables passed with
use
are inherited by value by default (they're copies). - If you want to modify the original variable inside the closure, you need to pass it by reference using
&
.
Example of passing by reference:
$count = 0; $increment = function() use (&$count) { $count ; }; $increment(); echo $count; // Outputs: 1
This behavior is cruel when you're building stateful closings or need to track changes outside the function itself.
Common Use Cases
You'll typically see closures and the use
keyword in these scenarios:
Array Functions : When filtering or mapping arrays.
$numbers = [1, 2, 3, 4]; $threshold = 2; $filtered = array_filter($numbers, function($n) use ($threshold) { return $n > $threshold; });
Event Handlers : In frameworks or libraries where callbacks are registered dynamically.
Stateful Callbacks : When maintaining some context across multiple calls without using global variables.
Creating Custom Sort Logic :
usort($users, function($a, $b) use ($sortBy) { return strcmp($a->$sortBy, $b->$sortBy); });
These examples show how closings help keep your code clean and focused on the task at hand.
So yeah, closings are a powerful feature in PHP, especially when combined with the
use
keyword. They let you write concise, localized logic without polluting the global namespace. Just remember: if you need external variables, always reach foruse
, and be mindful of whether you're passing by value or reference.Basically that's it.
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