Seven-Streams opened a new pull request, #684:
URL: https://github.com/apache/tvm-ffi/pull/684
# [Rust][Feat] Add runtime-checked casting between ObjectRef types
## Summary
Add runtime-checked casting between arbitrary `ObjectRef` types in the Rust
bindings, mirroring C++ `ObjectRef::as<T>` / `Downcast<T>`.
- **`ObjectRefCast`** (blanket impl for all `ObjectRefCore` types):
- `try_cast::<B>(self)` — consumes `self`, rewraps the object pointer
without
copying; fails with a `TypeError` naming both type keys.
- `cast_clone::<B>(&self)` — borrowing variant, shares ownership via
inc_ref.
- Succeeds iff the **runtime** type of the underlying object is
`B::ContainerType` or a subtype, so downcasting through a parent
reference
works as expected.
```rust
let base: TestBase = derived.try_cast()?; // upcast
let obj: ObjectRef = base.try_cast()?; // upcast to root
let d: TestDerived = obj.try_cast()?; // checked downcast
```
- **`is_instance_of(a_idx, b_idx)`** — O(1) subtype check via the
process-wide
type table (equal-index fast path + one ancestor-table lookup), the Rust
counterpart of C++ `IsObjectInstance`.
- **Hierarchy-aware `Any`/`AnyView` conversions**: derive-generated
`check_any_strict` / `try_cast_from_any_view` now use `is_instance_of`,
aligning with C++ `CheckAnyStrict` — converting an `Any` holding a derived
object to a parent reference (incl. `ObjectRef`) now succeeds.
- **Derive fixes** (uncovered by first external-crate use): generated code no
longer references `proc_macro_error`; `type_str()` return type fully
qualified; `object::unsafe_` made `#[doc(hidden)] pub`.
- **Tests**: `tests/test_cast.rs` covers multi-level up/downcast round-trips,
failure messages, refcounts, `Any` subtype conversions/rejections, and
leak-free destruction. Exact-match fast path unchanged (~1 compare); slow
path ~8ns, only on previously-failing paths.
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