Functions

By the end of this lesson you'll write reusable PHP functions with typed parameters and return types, default and named arguments, variadics, references, and arrow functions and closures — the building blocks of every program bigger than a script.

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Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ Defining, Calling & Returning

A function is a named block of code you can run on demand. You define it once with the function keyword, then call it by writing its name followed by () . A parameter is an input slot in the definition; an argument is the actual value you pass when calling. The keyword return hands a value back to whoever called the function — that's different from echo , which only prints. A return type like : string after the ) documents and enforces what comes back; : void means "returns nothing".

The declare(strict_types=1); line at the top makes PHP strict about types — pass a string where an int is expected and you get a clear error instead of a silent conversion. Put it at the very top of every file; it's a best-practice habit that catches bugs early.

2️⃣ Typed Parameters, Defaults & Named Arguments

Types in front of a parameter ( string $name ) say what kind of value is allowed. A default value ( $role = "Student" ) makes a parameter optional — leave it out and the default is used. A nullable type ?string means "a string or null ", and a union type int|string (PHP 8) means "either of these". With named arguments (PHP 8) you pass values by parameter name — introduce(role: "Mentor", name: "Carol") — so order stops mattering and your calls read like documentation.

3️⃣ Variadics & Pass-by-Reference

Sometimes you don't know how many arguments you'll get. A variadic parameter int ...$numbers collects every extra argument into one array, so sum(1, 2, 3) and sum(10, 20, 30, 40) both work. By default PHP passes a copy of each argument, so changing a parameter inside a function leaves the caller's variable untouched. Put an ampersand in front — &$total — to pass by reference instead, letting the function edit the original directly. Use references sparingly; usually returning a value is clearer.

4️⃣ Arrow Functions, Closures & Scope

PHP also lets you store a function in a variable — an anonymous function with no name. An arrow function fn($x) => $x * 2 (PHP 7.4+) is the short form: a single expression that automatically grabs any outer variables it mentions. A closure function ($x) use ($y) {' ... '} can hold a full multi-line body but must explicitly list outer variables in its use () clause. This matters because every function has its own scope : it can't see variables defined outside it unless you pass them in, capture them, or pull a global in with the global keyword.

5️⃣ Your Turn

Now you write the missing pieces. The script below is almost complete — fill in each ___ using the 👉 hint, then run it and check it against the Output panel.

One more — this time finishing an arrow function and a closure that needs to capture a variable.

📋 Quick Reference — PHP Functions

No code is filled in this time — just a brief and an outline. Write it yourself, run it on onecompiler.com/php or your own machine, then check your result against the expected output in the comments. This combines a variadic function, a return type, and a helper that formats the result.

Practice quiz

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