Void return types in PHP 7.1 ensure a function must not return any value, improving code clarity and preventing misuse. 1. Declaring a function with void means it should not return anything meaningful. 2. It can either return nothing or use an empty return to exit early. 3. Returning any value, including null, triggers a TypeError. 4. Void is useful for functions that perform actions like outputting data or modifying state without producing a result. 5. It works consistently regardless of strict or weak typing mode, enforcing no return value at runtime. 6. Common mistakes include unintentionally returning values, mixing void with nullable types, or confusing void with null. Using void makes code more predictable, self-documenting, and maintainable, especially in larger applications.

Void return types in PHP 7.1 mean that a function is not supposed to return any value at all. If you declare a function with void as its return type, it can either return nothing or just an empty return; statement. Trying to return a value will trigger a TypeError.

What does "void" actually do?

When you add void as a return type to a function, you're telling PHP (and anyone reading your code) that this function should not return anything meaningful. It might perform an action like printing output, modifying an object, or setting session data — but it doesn't give back a result.

For example:

function sayHello(): void {
    echo "Hello!";
}

This function works fine because it doesn’t try to return anything. But if you tried to do this:

function sayHello(): void {
    return "Hello!"; // This will cause a TypeError
}

PHP will throw an error during execution because you’re returning a string when the function promised not to return anything.

You can use an empty return:

function maybeSayHello(bool $shouldSay): void {
    if (!$shouldSay) {
        return; // perfectly okay
    }
    echo "Hello!";
}

That’s allowed because it's not returning a value — it's just ending the function early.

Why would you use void?

Using void helps make your code more predictable and self-documenting. If a function is meant to do something without producing a result, marking it as void makes that clear to others (or to your future self). It also prevents accidental misuse where someone might expect a return value.

Here are some common cases where void makes sense:

• Functions that output directly (like templates or responses)
• Event handlers or callbacks that don’t need to send back data
• Initialization routines that configure state but don’t compute values

It’s especially useful in larger applications or libraries where strong typing improves maintainability.

How does it fit with strict vs. weak typing?

In PHP 7.1, void return types work whether you're using declare(strict_types=1) or not — because void is always enforced strictly by design. Even in weak mode, returning a value from a void function will cause a runtime error.

So unlike other scalar types (like int or string), which only enforce type checks in strict mode, void is stricter no matter what.

What mistakes should you avoid?

A few things tend to trip people up when they start using void:

• ? Returning a value unintentionally:

  function logMessage(string $msg): void {
      return strlen($msg); // Not okay
  }

• ? Mixing void with nullable types:

  You can't write ?void or mix it with other types. It's not allowed — it either returns nothing or something else.

• ? Confusing void with null:

  A function returning null technically returns a value (NULL). So even that won't work with void.

If you want to return null, then ?bool, ?array, or another nullable type is what you need — not void.

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Basically, void is for functions that do work but don’t return results. It helps prevent bugs and makes your intentions clearer. Once you get used to it, it becomes a helpful tool in writing clean, expressive PHP code.

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