[MM] Add Dangerous.listAppendDestroy to the MetaModelica

[Adrian Pop]

PR: ​https://github.com/OpenModelica/OpenModelica/pull/7303

Note that if you do:

Dangerous.listAppendDestroy(constantList, anyList) you will get a segfault as you cannot write the end of a constant list to point to the second list.

[Karim Adbdelhak]

I basically have something like the following example (extremely simplified). Will this work? And if not, is there a way to make it work? The lists contain ComponentRef in my current implementation but that could also be smth else.

function test
  input ComponentRef i1;
  input ComponentRef i2;
  input UnorderedMap<Integer, list<...>> map;
protected
  list<...> list1, list2;
algorithm
  // if both are in the map merge them
  if UnorderedMap.contains(i1, map) and UnorderedMap.contains(i2, map) then
    list1 := UnorderedMap.get(i1, map);
    list2 := UnorderedMap.get(i2, map);
    Dangerous.listAppendDestroy(list1,list2);
    UnorderedMap.add(i1, list2);
    UnorderedMap.add(i2, list2); // is this needed?
  else
    // smth else
  end if;

end if;

[Adrian Pop]

it should be: list1 := Dangerous.listAppendDestroy(list1,list2);
as when list1 is empty I return list2.

[Adrian Pop]

It depends on how the lists in the UnorderedMap are created, if they are created via cons then is fine.

[Karim Adbdelhak]

They cannot be empty, they will always have at least one entry. And they are created step by step either by appending one element at a time or merged like we see here.

[Karim Adbdelhak]

Replying to adrpo:

it should be: list1 := Dangerous.listAppendDestroy(list1,list2);
as when list1 is empty I return list2.

Good to know! So list1 will be the list i have to use and whatever i put in i cannot use anymore right?

[Adrian Pop]

list1 will be destroyed if not empty, if is empty then list2 will be returned and list1 stays empty.

[Adrian Pop]

This is the C code for it, maybe is easier to understand how it works:

modelica_metatype listAppendDestroy(modelica_metatype lstFirstDestroyed, modelica_metatype listSecondKept)
{
  modelica_metatype lst = lstFirstDestroyed;
  if (MMC_NILTEST(lstFirstDestroyed)) {
    return listSecondKept;
  }
  while (!MMC_NILTEST(lst))
  {
    /* reached the end, set the element */
    if (MMC_NILTEST(MMC_CDR(lst)))
    {
      MMC_CDR(lst) = listSecondKept;
      break;
    }
    lst = MMC_CDR(lst);
  }
  return lstFirstDestroyed;
}

[Philip Hannebohm]

Since we are talking about performance here, does this save one if-statement?

modelica_metatype listAppendDestroy(modelica_metatype lstFirstDestroyed, modelica_metatype listSecondKept)
{
  modelica_metatype lst = lstFirstDestroyed;
  if (MMC_NILTEST(lstFirstDestroyed)) {
    return listSecondKept;
  }
  while (!MMC_NILTEST(MMC_CDR(lst))) {
    lst = MMC_CDR(lst);
  }
  /* reached the end, set the element */
  MMC_CDR(lst) = listSecondKept;
  return lstFirstDestroyed;
}

[Adrian Pop]

Sure, make a PR with it.

[Karim Adbdelhak]

Seems to work perfectly fine, thanks adrian!