code: public function classesByDirectory($directoryPath)
      {
          $this->typeCheck->classesByDirectory(func_get_args());
  
          $classDefinitions = array();
          foreach ($this->fileIterator($directoryPath) as $filePathInfo) {
              $classDefinitions = array_merge(
                  $classDefinitions,
                  $this->classesByFile($filePathInfo->getPathname())
              );
          }
  
          return $classDefinitions;
      }
docs: @param string $directoryPath
  
  @return array<ClassDefinition>