PHP type constraints

PHP 5 can use type constraints. The parameters of the function can be specified only for the object (the name of the class specified in the function prototype), and PHP 5.1 can be specified only as an array. Note that even if you use a type constraint, if you use NULL as the default value for the parameter, you can still use NULL as the argument when you call the function.

Type constraints only support both objects and arrays (after PHP 5.1). Integer and string types are not supported.

Incorrect use of String type constraints results in an error similar to the following:

Catchable fatal Error:argument 1 passed to Models_workflow_instance::getrand () must is an Instance of string, string give N

Detailed Example: http://us3.php.net/manual/zh/language.oop5.typehinting.php

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