You might thing that PHP is not able to automatically perform a type check on items in an array. But using variadic constructor this is possible. Bert Ramakers wrote a blogpost with some good examples on how to do this.

One of the language features announced back in PHP 5.6 was the addition of the “…” token to denote that a function or method accepts a variable length of arguments. Something I rarely see mentioned is that it’s possible to combine this feature with type hints to essentially create typed arrays.

https://medium.com/2dotstwice-connecting-the-dots/creating-strictly-typed-arrays-and-collections-in-php-37036718c921