Type declarations allow the type to be specified for properties, function parameters, and function return types. This permits the PHP engine to enforce that the specified types are used.
Argument Type Declarations
Early versions of PHP relied exclusively on proper documentation of functions for developers to know what arguments a function accepts. To allow for functions that are more robust, PHP 5 began to introduce argument type declarations, permitting the type of a function parameter to be specified. Valid types for type declarations are shown in Table 18-1, along with the PHP version ...
