Illuminate\Database\Query\Builder::when PHP Method

    public function when($value, $callback, $default = null)
    {
        $builder = $this;
        if ($value) {
            $builder = call_user_func($callback, $builder);
        } elseif ($default) {
            $builder = call_user_func($default, $builder);
        }
        return $builder;
    }

 /**
  * Apply the callback's query changes if the given "value" is true.
  *
  * @param bool $value
  * @param \Closure $callback
  * @return \Illuminate\Database\Query\Builder
  * @static
  */
 public static function when($value, $callback)
 {
     return \Illuminate\Database\Query\Builder::when($value, $callback);
 }