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1535 :: Error: expression has no address

• DSblizzard (orginal) [2015-08-13T19:52:19+02:00] view original

  Sorry for crossposting, but it seems this forum has much higher activity than SO.

  lines 11-12:

  proc last[T](ll: seq[T]): var T =
    return ll[high(ll)]
  Run

  line 118:

  if last(formula)["state"] == c_empty:
  Run

  Errors:

  main.nim(118, 12) Info: template/generic instantiation from here main.nim(12, 12) Error: expression has no address

  What the compiler wants?

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• EXetoC (orginal) [2015-08-13T19:58:00+02:00] view original

  It's nice to be reminded of any activity over there. It's a popular community and it would be beneficial to have more posts on stackoverflow.

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• DSblizzard (orginal) [2015-08-13T20:33:51+02:00] view original

  Thank you, error in this place has gone, but appeared in another:

  import tables
  
  
  type
    Tformula_elt = Table[string, int]
  
  proc empty_state(): var Tformula_elt =
    return toTable({"size": 0, "minus_count": 0, "state": 0})
  Run

  temp.nim(8, 17) Error: expression has no address

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• Araq (orginal) [2015-08-13T20:45:11+02:00] view original

  Nim is not C++, to create a mutable view via var T the location has to be mutable in the first place. In your first example the seq is not mutable since you don't use var seq in the second example toTable doesn't even return a location at all, how could you create a mutable view on it?

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• EXetoC (orginal) [2015-08-13T20:47:58+02:00] view original

  I don't think var is what you want here, and probably not in the previous code either. If you want the ability to mutate the returned variable then all you have to do is var x = empty_state() instead of let x = empty_state()

  EDIT: SO answer updated

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• DSblizzard (orginal) [2015-08-13T20:49:54+02:00] view original

  @Araq: "toTable doesn't even return a location at all". But how then can I change "size" of returned table in another procedure?

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• DSblizzard (orginal) [2015-08-13T20:55:24+02:00] view original

  OK, new trouble:

  import tables
  
  
  type
    Tformula_elt = Table[string, int]
  
  proc last[T](ll: var seq[T]): var T =
    return ll[high(ll)]
  
  proc empty_state(): Tformula_elt =
    return toTable({"size": 0, "minus_count": 0, "state": 0})
  
  proc symm_region_formulas(n: int): void =
    var formula = @[empty_state()]
    var d = addr(last(formula))
    d[]["size"] += 1
  Run

  temp.nim(16, 15) Error: type mismatch: got (int, int literal(1)) but expected one of: system.+=(x: var T, y: T) system.+=(x: var T, y: T)

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• Araq (orginal) [2015-08-13T20:57:38+02:00] view original

  proc foo: int = 8
  
  foo() = 3 # doesn't compile
  
  var f = foo()
  f = 3 # compiles
  Run

  So clearly the var/let declaration creates the location, not the call to foo.

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• Araq (orginal) [2015-08-13T21:01:05+02:00] view original

  tables.[] doesn't return a var T, tables.mget does.

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