code: func (c *Comm) getOrCreateMapping(channel string) MemberMapping {
  	// Lazily create a mapping if it doesn't already exist
  	mapping, exists := c.Chan2Members[channel]
  	if !exists {
  		mapping = make(MemberMapping)
  		c.Chan2Members[channel] = mapping
  	}
  	return mapping
  }
docs: // getOrCreateMapping creates a MemberMapping for the given channel
  // or returns the existing one.