🔁 PHP Passing Functions – Use Callables, Closures, and Callbacks Like a Pro

Learn how to pass functions as arguments in PHP using callables, closures, and arrow functions for dynamic and reusable code.

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🧲 Introduction – What Does “Passing Functions” Mean?

In PHP, you can pass a function to another function as an argument. This technique is commonly used for:

• Callbacks
• Sorting
• Filtering
• Custom logic injection

PHP supports this with callables, including named functions, anonymous functions, arrow functions, and object methods.

🎯 In this guide, you’ll learn:

• How to pass functions as arguments
• Using callables with call_user_func() and array_map()
• Passing anonymous and arrow functions
• Real-world examples and best practices

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✅ 1. Passing Named Functions as Arguments

function sayHello($name) {
    return "Hello, $name!";
}

function greetUser($callback, $name) {
    echo $callback($name);
}

greetUser("sayHello", "Alice"); // Hello, Alice!

📘 The string "sayHello" refers to the function name. PHP automatically resolves it as a callable.

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📦 2. Using call_user_func()

function welcome($msg) {
    echo "Welcome, $msg!";
}

call_user_func("welcome", "John"); // Welcome, John!

📘 call_user_func() lets you dynamically call any function or method.

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🔐 3. Passing Anonymous Functions

$log = function($message) {
    echo "[LOG]: $message";
};

function process($callback) {
    $callback("Processing started...");
}

process($log); // [LOG]: Processing started...

📘 Anonymous functions can be stored in variables and passed like regular data.

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🚀 4. Arrow Functions (PHP 7.4+)

$uppercase = fn($name) => strtoupper($name);

echo $uppercase("php"); // PHP

📘 Arrow functions are short, single-expression alternatives to closures.

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🔄 5. Real-World Example – Array Filtering with Callback

$nums = [1, 2, 3, 4, 5];

$even = array_filter($nums, function($n) {
    return $n % 2 === 0;
});

print_r($even); // [1 => 2, 3 => 4]

📘 array_filter() uses the passed function to determine which items to keep.

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🧬 6. Object Method as Callback

class Logger {
    public function write($msg) {
        echo "LOG: $msg";
    }
}

$logger = new Logger();
call_user_func([$logger, 'write'], "System started"); // LOG: System started

📘 Methods can be passed using [$object, 'methodName'] syntax.

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🔗 Callable Types in PHP

Type	Syntax	Example
Named function	"functionName"	"strlen"
Anonymous	function($x){}	See above
Arrow function	fn($x) => $x + 1	Short syntax
Static method	['ClassName', 'method']	['MathUtils', 'add']
Object method	[$obj, 'method']	[$logger, 'write']
Invokable object	new class { function __invoke() {} }	Used like a function

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🧠 Best Practices

• ✅ Use arrow functions for short callbacks
• ✅ Validate callables using is_callable() before executing
• ✅ Keep passed functions focused and pure (no side effects)
• ✅ Use descriptive names for anonymous functions
• ❌ Avoid deep nesting of callbacks — use named functions if needed

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📌 Summary – Recap & Next Steps

Passing functions in PHP helps write flexible, DRY, and modular code. It’s widely used in sorting, filtering, validation, and event-driven logic.

🔍 Key Takeaways:

• PHP supports passing functions using callables
• Use call_user_func() or pass directly to higher-order functions
• Arrow and anonymous functions are powerful tools for inline logic
• Callable arrays let you use object and static methods dynamically

⚙️ Real-World Use Cases:
Form validation, data transformation, custom sorters, logger hooks, middleware layers.

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❓ Frequently Asked Questions (FAQs)

❓ What is a callable in PHP?
✅ Any function, method, closure, or arrow function that can be invoked.

❓ Can I pass class methods as arguments?
✅ Yes. Use [$object, 'method'] for instance methods, or ['ClassName', 'method'] for static methods.

❓ What’s the difference between closures and arrow functions?
✅ Closures can have multiple statements and use use() for scope. Arrow functions are shorter and auto-inherit variables.

❓ Can I check if a function is callable before using it?
✅ Yes. Use is_callable($func).

❓ Can I return a function from another function?
✅ Yes, you can return a closure or arrow function from a function.

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