scovich commented on PR #7843:
URL: https://github.com/apache/arrow-rs/pull/7843#issuecomment-3032633370
> > **Against**: Outside unit tests, recursive builders will almost always
live in a nested scope vs. their parent -- usually a called function or method,
or at least a `match` clause -- which would trivially defeat the drop sentinel.
>
> I don't understand what you mean by defeat the drop sentinel. Since the
`ObjectBuilder` has a `mut` reference to its parent, I don't think the rust
compiler will allow anything to the same underlying parent builder
>
> Maybe I am missing something here and an example would help 🤔
From what I understood, the example you gave above would trivially defeat an
`impl Drop` sentinel (= empty `drop` method), because the `object_builder` goes
out of scope before the call to `list_builder.finish()`:
```rust
let mut builder = VariantBuilder::new();
let mut list_builder = builder.new_list();
{
let mut object_builder = list_builder.new_object();
object_builder.insert("id", 1);
// NOTE object_builder.finish() is not called here
}
list_builder.finish();
let (metadata, value) = builder.finish();
```
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