stdClass and type hinting

Question

$obj = new stdClass();
echo gettype($obj); //object

function abc(object $obj) {
    return;
}

abc($obj); //Catchable fatal error: Argument 1 passed to abc() must be an instance of object, instance of stdClass given

Why calling abc($obj) triggers error?

Catchable fatal error: Argument 1 passed to abc() must be an instance of object, instance of stdClass given

Answer 1

Because type hinting works only for class name, interface name or array. There is no common ancestor object (like in some other programming languages like C#) in php object model. What you have to specify is stdClass

As of php 7.2 it's now possible to use object type hint exactly as you guessed in your question:

function abc(object $obj) {
    return;
}

Answer 2

Read the documentation about type hinting in PHP. Your current code forces abc function to accept a parameter that is an instance of the class object (a class named object!). Do that instead:

function abc(stdClass $obj)