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Auto generated destructors for tuples/objects fail with "non-trivial" error... #11671

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GordonBGood opened this issue Jul 6, 2019 · 0 comments

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@GordonBGood
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commented Jul 6, 2019

There are times one wants to call the auto generated =destroy destructor for generic types without being concerned about what types they are or what types they contain. For example, one might define a type that might contain primitive types such as numbers, enum's, set's, proc's, but might also contain pointer's, ptr's, ref's or nested tuples/objects. Currently, one can't just call the =destroy destructor assuming that it will be auto generated correctly.

Example

type
  TestObj = object
    a, b: int

# following fails with:  Error: internal error: destructor turned out to be not trivial
# var tst0 = (1, 2); tst0.`=destroy`
# following fails with:  Error: internal error: destructor turned out to be not trivial
# var tst1 = TestObj(a: 1, b: 2); tst1.`=destroy`

Expected Output

It should just destroy as @Araq has said it should, destroying each of the fields

Possible Solution

One needs to define a "deepDestroy" overloaded series of proc's as follows and call that from within a custom =destroy destructor to bypass the current behavior:

# this builds stack, but is unlikely to recurse deep enough to cause stack overflow...
# this appears to be the only way to ensure that nested structures containing a combination of
# pointers, (can also be ref's), tuples and objects...
proc deepDestroy[T: SomeNumber | enum | set | proc](x: var T) {.inline.} = discard
proc deepDestroy[T: object | tuple](x: var T) {.inline.} =
  for e in x.fields:
    var ev = e; ev.deepDestroy; x.reset
proc deepDestroy[T: pointer](x: var T) {.inline.} =
  if x != nil: x.dealloc; x.reset
proc deepDestroy[T](x: var ptr T) {.inline.} =
  if x != nil: x[].deepDestroy; x.dealloc; x.reset
proc deepDestroy[T](x: var ref T) {.inline.} =
  if x != nil: x[].deepDestroy; x.reset

Additional Information

  • Your Nim version: 0.20.0
  • Was it working in the previous Nim releases? Don't know, but destructors are quite a new feature

@Araq Araq closed this in 3258c1e Jul 6, 2019

narimiran added a commit that referenced this issue Jul 8, 2019

fixes #11671
(cherry picked from commit 3258c1e)
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