code: func (c *Cache) RegisterType(n string, typ Type, opts *RegisterOptions) {
  	if opts == nil {
  		opts = &RegisterOptions{}
  	}
  	if opts.LastGetTTL == 0 {
  		opts.LastGetTTL = 72 * time.Hour // reasonable default is days
  	}
  
  	c.typesLock.Lock()
  	defer c.typesLock.Unlock()
  	c.types[n] = typeEntry{Type: typ, Opts: opts}
  }
docs: // RegisterType registers a cacheable type.
  //
  // This makes the type available for Get but does not automatically perform
  // any prefetching. In order to populate the cache, Get must be called.