GSoC Rust UNO API Weekly Update 9

[Mohmed Ali]

*Hi all,*

Here’s a quick update outlining the progress from *Week 9* of the Rust–UNO
binding project.

Last week, I worked on handling *edge cases* in the generated code. I’ll
also summarize what we have been doing over the past weeks regarding the
generated code:

   -

   When calling *C++ logic via FFI*, we found that we must wrap it in *C
   functions or C-compatible types* (e.g., structs, enums).
   -

   To address this, we relied on *XInterface* (the base interface for all
   UNO interfaces). We pass it as a parameter, cast it to the required
   interface, and then call the target method.
   -

   Since Rust *traits* cannot be directly used across FFI boundaries, we
   always evaluate whether something can safely cross FFI before implementing
   it.
   -

   For other *core UNO types*, we used their *internal pointers* to pass
   values between Rust and C. We then cast those pointers to the corresponding
   C++ types (e.g., rtl_uString and OUString).
   -

   As Rust does not support *inheritance for structs*, we handled this by
   using *composition* in the parent struct instead.

Here’s an example of what we discussed:
```
/// FFI bridge for ooo.vba.excel.XRange::Address
rtl_uString* Address_(
    XInterface* pInterface,
    uno_Any* RowAbsolute,
    uno_Any* ColumnAbsolute,
    uno_Any* ReferenceStyle,
    uno_Any* External,
    uno_Any* RelativeTo
)
{
    if (!pInterface)
        return nullptr;

    try
    {
        Reference<ooo::vba::excel::XRange> xInterface(pInterface,
UNO_QUERY_THROW);

        auto result = xInterface->Address(
            *reinterpret_cast<Any*>(RowAbsolute),
            *reinterpret_cast<Any*>(ColumnAbsolute),
            *reinterpret_cast<Any*>(ReferenceStyle),
            *reinterpret_cast<Any*>(External),
            *reinterpret_cast<Any*>(RelativeTo)
        );

        // Convert OUString result to rtl_uString*
        return result.pData;
    }
    catch (const Exception& e)
    {
        SAL_WARN("codemaker.rustmaker", "Exception in FFI bridge function");
        (void)e;
        return nullptr;
    }
}
```

*Next steps:*


   -

   Continue handling *edge cases* in the generated code.
   -

   Expand support for *core UNO types*.

Best,
Ali
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