array_unshift() expects parameter 1 to be array, null given

Question

I want to add data to my array using array_unshift() but it shows " array_unshift() expects parameter 1 to be array, null given "

here is my code:

public function index($child = null)
{
    $crumbs = [];

    function getParents($id){
        $parent = Instrument::where('id', $id)->first(['id', 'title', 'parent']);

        if($parent->parent != null){
            array_unshift($crumbs, $parent);
            getParents($parent->parent);
        }
    }

    if($child != null){ 
        getParents($child);
    }
    
    //return code here
}

do you have any solution?

BTW, I am using Laravel 8, PHP 7.4.13

Answer 1

Variable $crumbs isn't visible in getParents function.

So you should pass it as an argument or make it a global variable or make a property for an object.

public function index($child = null)
{
    $crumbs = [];

    function getParents($id, &$crumbs){
        $parent = Instrument::where('id', $id)->first(['id', 'title', 'parent']);

        if($parent->parent != null){
            array_unshift($crumbs, $parent);
            getParents($parent->parent);
        }
    }

    if($child != null){
        getParents($child, $crumbs);
    }

    //return code here
}

For example like this.