PHP：无法将Object分配给数组

I have create the following class :

Main class file

class NativeTabs
{
    private $tabs = array();

    public function __construct()
    {
        require_once('/options_elements.php');
    }

    public function add_tab($key = '', $name = '')
    {
        // ...

        $this->tabs[$key] = $name;
        $this->tabs[$key][] = new OptionsElements();

        // ...

    }
}

$nt = new NativeTabs();
$nt->add_tab('tabname', "Tab Name");

options_elements.php File

class OptionsElements
{
    public function __construct()
    {
    }
}

And when I execute that code I get the following error :

Fatal error: [] operator not supported for strings in PATH/TO/MY/FILEnative_tabs.php on line THE_LINE_THAT_CONTAIN_THE_CODE($this->tabs[$key][] = new OptionsElements();)

Why I can't assing the object in $this->tabs[$key][] ?

Any idea please ?

You should do

$this->tabs[$key] = array();
 $this->tabs[$key][] = new OptionsElements();

otherwise you use [] with a string (you assigned $this->tabs[$key] = $name; on the line above so $this->tabs[$key] is a string)

Why should you be able to assign that?

$this->tabs[$key] = $name;

Judging by the name you just set the array element to a string. Then you try to append an array element to this string? That won't work.

$this->tabs[$key] is a string, not an array.

You can't add an item to a string as if it was an array.

This will work without errors.

$this->tabs[$key] = array("name");
$this->tabs[$key][] = new OptionsElements();

See inline.

$this->tabs[$key] = $name;
// $this->tabs[$key] becomes a string that contains $name
$this->tabs[$key][] = new OptionsElements();
// $this->tabs[$key][] has no meaning here as its neither array nor an unset value. 
// if it was unset or not declared PHP would have make it an array.

You could you the following.

$this->tabs[$key]['name'] = $name;
$this->tabs[$key]['option_elements'] = new OptionsElements();