PHP namespace error?

Question

PHP 5.6

This code:

<?php

namespace Database
{
    abstract class Model
    {

    }
}

namespace Models
{
    use Database\Model as DbModel;

    class Model extends DbModel
    {

    }
}

namespace Models
{
    use Database\Model;

    class Brand extends Model
    {

    }
}

namespace
{
    $m = new \Models\Model();
}

causes an error:

"Fatal error: Cannot use Database\Model as Model because the name is already in use in D:\OpenServer\domains\localhost\index.php on line 23".

This code:

<?php

namespace Models
{
    use Database\Model as DbModel;

    class Model extends DbModel
    {

    }
}

namespace Models
{
    use Database\Model;

    class Brand extends Model
    {

    }
}

namespace Database
{
    abstract class Model
    {

    }
}


namespace
{
    $m = new \Models\Model();
}

has no errors.

Why is this happening? Because the code has not been changed.

Answer 1

The ordering of your namespace clauses makes the difference here; in the first example, the Database namespace clause is declared before the clause that defines the class Models\Model.

A similar example of that difference can be found in the documentation:

(...) However, the next example causes a fatal error on name conflict because MyClass is defined in the same file as the use statement.

Separate files or same file here is simulated by moving the Database namespace below or above, respectively.

That said, the documentation also states:

It is strongly discouraged as a coding practice to combine multiple namespaces into the same file. The primary use case is to combine multiple PHP scripts into the same file.

Update

Interestingly, this problem is what Drupal 8 developers recently found out as well, but according to this bug report it has been reported more than two years ago.

A pull request has been submitted to address this issue for the next major version (it may be back ported to 5.x as well).

Answer 2

After few tests: PHP file with few namespaces behave difficult to understand, try to do not use more then one namespace in one file.

(It's because of linking to not existing classes while parsing [of one file!] that change order of PHP parsing, C++ things [pointers] - I can't explain that.)

As PHP doc says: "It is strongly discouraged as a coding practice to combine multiple namespaces into the same file."

More about tests I did and documentation we studied to find it out:

https://chat.stackoverflow.com/rooms/71776/discussion-between-axiac-and-jack