为什么我的函数不返回字符串？

Question

I have a function that first looks for premium brands to add to a string. If there is not enough premium brands, it continues and ads non-premium brands (max 4 brands).

I'm able to echo the string inside the function and it shows 4 brands, but I'm not able to return the string. Why is that?

$bnames = addBrandNameToTitle($model);
echo $bnames; // This is empty

function addBrandNameToTitle($model, $brandNames = array(), $ispremium = true){
    if($ispremium):
        foreach ($model->brands as $brand):
            if ($brand->isPremium() && count($brandNames)  < 4):
                array_push($brandNames, $brand->name);
            endif;

            if(count($brandNames)  >= 4){
                return implode(',', $brandNames);
            }
        endforeach;
        // If not enough premium, add non-premium brands
        addBrandNameToTitle($model, $brandNames, false);
    else:
        foreach ($model->brands as $brand):
            if (!$brand->isPremium() && count($brandNames) < 4):
                array_push($brandNames, $brand->name);
            endif;
        endforeach;
        $bnames = implode(',', $brandNames);
        echo $bnames; // <-- This lists 4 brands
        return $bnames; // <-- But this is not returning the string. Why?
    endif;
}

Answer 1

In this section of code, you forgot to return the value

// If not enough premium, add non-premium brands
return addBrandNameToTitle($model, $brandNames, false);  // Add a return