code: public function setSingletons(array $singletons)
      {
          foreach ($singletons as $class => $definition) {
              if (is_array($definition) && count($definition) === 2 && array_values($definition) === $definition) {
                  $this->setSingleton($class, $definition[0], $definition[1]);
                  continue;
              }
  
              $this->setSingleton($class, $definition);
          }
      }
docs: Registers class definitions as singletons within this container by calling [[setSingleton()]].
  
  @param array $singletons array of singleton definitions. See [[setDefinitions()]]
  for allowed formats of array.
  
  @see setDefinitions() for allowed formats of $singletons parameter
  @see setSingleton() to know more about possible values of definitions
  @since 2.0.11