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1062 :: Instance Variables Accessed From Template

• leepysham (orginal) [2015-03-23T16:25:43+01:00] view original

  Hi, it seems that one can access instance variables that are supposed to be hidden when using immediate templates. Is this behavior intended? If so, why is this the case, and what other scope-related pitfalls should I be aware of?

  # B.nim
  
  type T* = object
      a: int
  
  proc createT*(x: int) : T =
      result.a = x
  
  proc b(t: T) : int = t.a
  
  
  template doAction*(action: stmt) {.immediate.} =
      action
  Run

  # A.nim
  
  import B
  
  var t = createT(3)
  
  doAction:
      t.a += 1  # this works
      echo t.a  # this works
      echo t.b  # this doesn't work (as expected)
  Run

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• Araq (orginal) [2015-03-23T17:00:48+01:00] view original

  This is supported so that template accessor*(x: T): int = x.a can work. But maybe we should support that differently to prevent your code example from compiling.

  and what other scope-related pitfalls should I be aware of?

  This question is impossible to answer. Feature vs bug is a difficult question when it comes to scoping rules in a macro system.

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• leepysham (orginal) [2015-03-23T17:27:56+01:00] view original

  Thank you for the explanation. Do you know of any simple way around this? The reason I use an immediate template is so that I can do things like this:

  template doSomething*(v: expr, s: stmt) {.immediate.} =
      let `v` {.inject.} = ...
      s
      finalize
  Run

  Currently, the two options that I know of are just to keep it as is and hope no confusion arises, or move T to a new file and export it from B.

  # B_private.nim
  
  type T* = object
      aval : int
  
  proc a*(t: T) = t.aval
  
  proc `a=`*(t: var T, k: int) = t.aval = k
  Run

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