asset not working in laravel

php artisan cache:clear
php artisan route:cache
php artisan config:cache
php artisan view:clear

if (! function_exists('asset')) {
    /**
     * Generate an asset path for the application.
     *
     * @param  string  $path
     * @param  bool    $secure
     * @return string
     */
    function asset($path, $secure = null)
    {
        return app('url')->asset("public/".$path, $secure);
    }
}