abstract-override1.php

<?php

abstract class A
{
    abstract function test(string $s);
}

abstract class B extends A
{
    abstract function test($s) : int;
}

abstract-override2-error.txt

Fatal error: Declaration of B::test(string $s): int must be compatible with A::test($s)

abstract-override2.php

<?php
abstract class A
{
    abstract function test($s);
}

abstract class B extends A
{
    abstract function test(string $s) : int;
}

object-type.php

<?php

function test(object $obj): object
{
    echo 'Param is type of: ', gettype($obj), nl2br("\n");
    return new SplQueue();
}

$result = test(new StdClass());
echo 'Return is type of: ', gettype($result), nl2br("\n");

// Print
// Param is type of: object
// Return is type of: object

parameter-type-widening.php

<?php

interface A
{
    public function test(array $input);
}

class B implements A
{
    public function test($input) {}
}