PHP has been supporting type-hints on complex types for quite some time already: PHP 5.0 for objects, 5.1 for array and 5.4 for callable. The question of extending this support to scalar types (integer, float, boolean and string) as been discussed several times those last years, each time with a bit more support.

http://blog.pascal-martin.fr/post/in-favor-of-rfc-scalar-type-hints.html