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1851 :: How do you create a reference to an sequence or object?

• enjoysmath (orginal) [2015-12-06T23:48:57+01:00] view original

  
      var fv = tree.free_vars
      fv.add(op)
      echo "fv = ", fv
  Run

  tree.free_vars.add(op) wouldn't work: nim needed a var, so I created one, but it makes a copy of the sequence leaving the original unmodified (undesired).

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• Arrrrrrrrr (orginal) [2015-12-06T23:55:11+01:00] view original

  add(tree.free_vars, op)

  Run

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• enjoysmath (orginal) [2015-12-07T00:00:11+01:00] view original

  @Arrrrrrrr, that doesn't work because nim wants a var instead of just a plain seq (tree.free_vars) whatever that means...

  Here:

  
  expr_tree.nim(272, 8) Error: type mismatch: got (seq[Op], Op)
  
  but expected one of:
  
  system.add(x: var seq[T], y: T)
  Run

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• Arrrrrrrrr (orginal) [2015-12-07T00:05:45+01:00] view original

  Well, i dont know how do you declared tree or what is free_vars exactly:

  • If tree is an object, it shouldn't be defined like let tree = Tree(whatever), but var tree = Tree(whatever). If tree is a ref object you can ignore this
  • If free_vars is a proc, make sure the return type is var seq[Op]: proc tree_vars(t: Tree): var seq[Op]

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• enjoysmath (orginal) [2015-12-07T00:09:22+01:00] view original

  
    ExprTree* = ref object
      root : Op
      free_vars : seq[Op]
  Run

  ref object on ExprTree seems to have gotten rid of complaint. I suppose to I could declare the tree param var?

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• Arrrrrrrrr (orginal) [2015-12-07T00:27:45+01:00] view original

  Then probably it didn't work because you created ExprTree like let tree = ExprTree() instead of var tree ExprTree():

  type MyType = object
    mySeq: seq[int]
  
  let mt1 = MyType(mySeq: @[])
  var mt2 = MyType(mySeq: @[])
  
  add mt1.mySeq, 0 # Error, mt1 is let
  add mt2.myseq, 0 # Works fine, it is a var
  Run

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• jibal (orginal) [2015-12-07T05:38:55+01:00] view original

  enjoysmath: whatever that means...

  var means mutable, let means immutable.

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