Forwarding references

gistfile1.nim

type Connection = object
  userName: string
  messageHistory: list[string]

type ConnectionManager = object
  networkConnections: map[string, Connection]

const
  NULL_CONNECTION : Connection = ...

# The Connection values could not be really copied. Maybe, I should use just var here?
proc getConnection(m: var ConnectionManager, host: string): Connection =
  return m.networkConnections[host]

# If I use the NullObject pattern, returning var type becomes harder? 
proc getUserConnection(m: var ConnectionManager, user: string): Connection =
  for host, con in items(networkConnections)
    if con.userName == user
      return con

  return NULL_CONNECTION

var gConnectionManager : ConnectionManager

# Let's assume that the list of messages is expensive to copy and we don't want to do it
proc getUserMessages(user: string) : list[string] =
  gConnectionManager.getUserConnection(user).messageHistory

# Multiple bodies of the function are compiled for the two usage patterns?                                     

let messages1 = getUserMessages("Araq") 
# just passes the reference

var messages2 = getUserMessages("Araq") 
# creates/initializes a copy 
# or a copy is created by the returned reference?


proc getUserName(host: string) : string =
  gConnectionManager.getConnection(host).nameName

proc getMostActiveUser(): string =
  var mostActiveHost = "foo" & "bar" & baz # this a temporary created local string
  return getUserName(mostActiveHost)

# This can not be safely optimized with the crude rules
# mostActiveHost in the body of getMostActiveUser is a temporary varialbe 
# passed to a function that could return it (so, reference could not be forwarded)
let user = getMostActiveUser()