PHP7.2中的新功能（参数类型声明）

class MyClass {
    public $var = 'Hello World';
}
$myclass = new MyClass;
function test(MyClass $myclass){
    return $myclass->var;
}
echo test($myclass);

Fatal error: Uncaught TypeError: Argument 1 passed to test() must be an instance of MyClass, string given, called in /app/index.php on line 12 and defined in /app/index.php:8

class MyClass {
    public $var = '';
}
class FirstChild extends MyClass {
    public $var = 'My name is Jim';
}
class SecondChild extends MyClass {
    public $var = 'My name is John';
}
$firstchild = new FirstChild;
$secondchild = new SecondChild;
function test(object $arg) {
    return $arg->var;
}
echo test($firstchild);
echo test($secondchild);

class MyClass {
    public $var = 'Hello World';
}
$myclass = new MyClass;
function test(MyClass $arg) : object {
    return $arg;
}
echo test($myclass)->var;

Fatal error: Uncaught TypeError: Return value of test() must be an instance of object, instance of MyClass returned in /app/index.php:10

<?php
class MyClass {
    public function myFunction(array $myarray) { /* ... */ }
}
class MyChildClass extends MyClass {
    public function myFunction($myarray) { /* ... */ }
}

Warning: Declaration of MyChildClass::myFunction($myarray) should be compatible with MyClass::myFunction(array $myarray) in %s on line 8