The case of unwanted copies

gistfile1.nim

# While programming in nimrod, I often miss the reference types from c++

# Consider this example:
type CompositeObject = object
  unwantedCopy: string
  expensiveToCopy: list[matrix]
  impossibleToCopy: map[string, TNetworkConnection]

proc properAccessor(o: var CompositeObject) : var string = 
  return o.unwantedCopy

proc clientCode = 
  ...
  var o : CompositeObject = ...
  var s = o.properAccessor # unwanted copy here, I just want to read from the value

# The situation gets worse with the other more expensive fields. 
# There will also be fields values for which defining a sensible copy semantics will 
# be problematic (e.g. TNetworkConnection)

# Example 2: Using references to avoid repeating complex expressions
proc wordCounter = 
  ...
  var wordCountData = knownWords[word]

  inc wordCountData.counter
  wordCountData.addOccurrence(currentLine, currentColumn)