PHP Default Arguments – Simplify Functions with Optional Parameters

Learn how to use default values in PHP function parameters to make your functions more flexible and maintainable.

Introduction – What Are Default Arguments in PHP?

Default arguments allow you to assign a predefined value to a function parameter, so it becomes optional during function calls. If no value is provided for that parameter, PHP uses the default value.

In this guide, you’ll learn:

• Syntax for using default values in function parameters
• How to mix required and optional arguments
• Use cases for simplifying function calls
• Best practices to avoid common pitfalls

Basic Syntax of Default Arguments

function greet($name = "Guest") {
    echo "Hello, $name!";
}

greet();         // Hello, Guest!
greet("Alice");  // Hello, Alice!

If no argument is passed, the default "Guest" is used.

Combining Required and Optional Parameters

function sendMessage($to, $message = "Hello") {
    echo "To: $to – $message";
}

sendMessage("John"); // To: John – Hello

Required parameters must always come before optional ones.

Multiple Default Arguments

function orderPizza($type = "Margherita", $size = "Medium") {
    echo "$size $type Pizza";
}

orderPizza();                     // Medium Margherita Pizza
orderPizza("Pepperoni", "Large"); // Large Pepperoni Pizza

You can define multiple default values in order.

Incorrect Parameter Order

//  Error: optional before required
function invalid($optional = "X", $required) {}

Fix:

function valid($required, $optional = "X") {}

Default Arrays and Booleans

function logMessage($text, $flags = []) {
    if (in_array("uppercase", $flags)) {
        $text = strtoupper($text);
    }
    echo $text;
}

logMessage("hello", ["uppercase"]); // HELLO
logMessage("hello");                // hello

Use arrays or booleans as default parameters for customizable behavior.

Best Practices

• Keep default values simple and static
• Use default arguments to reduce repetitive function calls
• Avoid putting required parameters after optional ones
• Document what default values are used for clarity

Summary – Recap & Next Steps

Default arguments make PHP functions more convenient by allowing flexible usage without breaking code structure. They are especially useful when dealing with optional settings or values.

Key Takeaways:

• Default arguments make parameters optional
• Defaults are used only when values are not passed
• Required parameters must come first
• Use with booleans, strings, arrays, or null values

Real-World Use Cases:
Email templates, logging functions, API wrappers, pagination, settings forms.

Frequently Asked Questions (FAQs)

Can I set the default value to null?
Yes, and you can check it inside the function using is_null().

What happens if I pass null to a default argument?
The value null overrides the default, but the function receives it explicitly.

Can default arguments be arrays?
Absolutely. Example: function getItems($filters = []) {}

Do named arguments work with default values?
Yes! Named arguments allow skipping optional parameters.