wip: structural map

[Kathryn-cat]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces the StructuralMapper and StructuralMapperObj APIs in include/tvm/ffi/extra/structural_map.h to support structural mapping and in-place mutation of object-backed values. It also adds corresponding custom hooks (kStructuralMap and kStructuralInplaceMutate), registers test leaf objects, and includes comprehensive unit tests. The review feedback suggests two minor optimizations in structural_map.h: avoiding a const_cast when obtaining the field address, and reusing the calculated field address instead of recalculating it for the field setter.

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[gemini-code-assist]

Since new_obj is a non-const pointer (Object*), we can avoid the const_cast on field_addr by declaring it as void* and using reinterpret_cast<char*>(new_obj).

        void* field_addr = reinterpret_cast<char*>(new_obj) + field_info->offset;
        int ret_code = field_info->getter(field_addr,
                                          reinterpret_cast<TVMFFIAny*>(&field_value));

[gemini-code-assist]

We can reuse the field_addr variable calculated earlier at line 508 instead of redundantly recalculating it as new_field_addr here.

        ret_code = reflection::CallFieldSetter(field_info, field_addr,
                                               reinterpret_cast<const TVMFFIAny*>(&new_field));