PSR-0 Argument passed

Catchable fatal error: Argument 1 passed to Core\Model\Mapper\PostMapper::save() must be an instance of Core\Model\Mapper\Post, instance of Core\Model\Post given, called in C:\wamp\www\Test\index.php on line 16 and defined in C:\wamp\www\Test\Core\Model\Mapper\PostMapper.php on line 15

index.php

<?php
require_once 'Core/Library/SplClassLoader.php';

$loader = new SplClassLoader('Core', '');
$loader->register();

use Core\Model\Post,
    Core\Model\Mapper\PostMapper;

$db = false;

$postMapper = new PostMapper($db);

$post = new Post;

$postMapper->save($post);

The PostMapper interface and PostMapper does have "Post"

<?php
namespace Core\Model\Mapper;

interface PostMapperInterface
{

    public function save(Post $post);
}

I can't understand why it is complaining about not being a "Post"

Solution

It is a Post, but not the Post it is looking for.

You seem to be confused by the namespaces. On one occation, Post refers to Core\Model\Mapper\Post, but what you pass is of type Core\Model\Post.

namespace Core\Model\Mapper;

interface PostMapperInterface
{

    public function save(Post $post);
}

You first state that you are now inside the namespace Core\Model\Mapper, so when you refer to Post in the method declaration, Post is relative to that namespace, which is why it wants an instance of the type Core\Model\Mapper\Post.

You need to change your code like this:

public function save(\Core\Model\Post $post);