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How can I enforce strict typing in PHP using declarations?

Hey everyone,

I've been working on a PHP project recently, and I'm trying to ensure strict typing in my codebase. I've heard that PHP 7 introduced a feature called "declarations" that can help with enforcing strict typing. However, I'm not quite sure how to utilize this feature effectively.

From what I understand, declaring types for function parameters and return values can help prevent any unexpected type mismatches and improve code reliability. But I haven't really used this feature before, so I'm a bit lost on where and how to start.

Could someone please guide me on how to enforce strict typing using declarations in PHP? It would be great if you could provide some examples or code snippets to illustrate the process. Any additional tips or best practices to keep in mind would also be highly appreciated.

Thanks in advance for your help!

All Replies


Hey there,

Enforcing strict typing in PHP using declarations is indeed a great practice to improve the reliability and maintainability of your code. I've worked with PHP for a while and have personally found this feature to be quite handy.

To start, you'll need to ensure that you're using PHP 7 or later, as this feature was introduced in PHP 7. You can specify the types of function parameters by adding a colon after the parameter name and then mentioning the type. Likewise, you can declare the return type by using a colon at the end of the function signature, followed by the desired type.

Here's an example to demonstrate this:

function calculateSum(int $a, int $b): int {
return $a + $b;

$result = calculateSum(5, 10); // This is valid
//$result = calculateSum(5.5, 10); // This will throw a TypeError

echo $result;

In this example, I've declared the types for the `calculateSum` function parameters as `int` and specified the return type as `int`. This will ensure that only integers are accepted as arguments and the function will always return an integer. If you were to pass a non-integer value, like a float in the commented line, PHP would throw a `TypeError`.

Using strict typing declarations helps catch potential issues early on and provides clearer documentation for future developers working on your code. It's especially useful when collaborating in a team, as it reduces the chances of type-related bugs and makes the code easier to comprehend.

Do keep in mind that strict typing declarations only apply to scalar types (int, float, string, and bool) and not to class/interface types. There are other techniques available to enforce stricter typing for classes/interfaces, such as type-hinting the object or using PHPDoc annotations.

I hope this explanation helps you get started with enforcing strict typing in PHP using declarations! Let me know if you have any further questions.



Enforcing strict typing using declarations in PHP has been a game-changer for me. As a PHP developer, it has immensely improved the robustness and maintainability of my codebase.

When it comes to strict typing, PHP 7 introduced the `declare(strict_types=1)` directive, which needs to be placed at the beginning of each relevant PHP file. This directive enables strict mode for the entire file, meaning that all the function parameters and return types will be checked against their specified types.

To illustrate this, consider the following example:


function multiply(int $a, int $b): int {
return $a * $b;

$result = multiply(5, '10'); // This will now throw a TypeError

echo $result;

Here, with the `declare(strict_types=1)` directive, passing a string `'10'` as the second argument to `multiply` function will result in a `TypeError`. PHP will ensure that the types are strictly adhered to, preventing unexpected type mismatches.

In my experience, enforcing strict typing using declarations has saved me countless hours of debugging and improved the overall stability of my projects. It also enhances code readability and reduces the need for excessive type-checking within function bodies.

One thing to remember is that strict typing doesn't automatically cover class properties or class method arguments. To enforce strict typing within classes, you can use type hints in method signatures and properties, including scalar types as well as custom class/interface types.

Overall, strict typing using declarations in PHP has been a valuable addition that I highly recommend incorporating into your development workflow. It may take some adjustment at first, but the benefits it brings to your codebase make it well worth the effort.

Feel free to ask if you have any further queries. Happy coding!

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