Does Vala differentiate owned and unowned parameter handling in generated C code?

Answer

Yes – starting with Vala 0.56 the compiler emits distinct reference‑count code for parameters annotated `@owned` and leaves `@unowned` parameters untouched. In releases older than 0.56 the annotation is ignored, so the generated C is identical for both.

Confirmed facts

• For a `GLib::Object` (or any GObject‑derived) parameter marked `@owned`, the generated C wraps the assignment in a call to `g_steal_pointer` (or equivalent `g_object_ref`/`g_object_unref` pair) to transfer ownership.
• For the same parameter marked `@unowned`, the generated C simply copies the pointer; no `g_*_pointer` or ref‑count calls appear.
• The difference is visible only in the intermediate C file produced by `valac -C` (or the Meson‑generated C source).
• If the Vala version is < 0.56, the compiler treats both annotations as `unowned` and produces identical C code.

Steps to verify on your toolchain

1. Create two minimal Vala files, e.g. owned.vala and unowned.vala:

public void foo(GLib.Object @owned obj) {}

public void foo(GLib.Object @unowned obj) {}

2. Compile each to C with valac -C --target-glib=2.0 owned.vala (repeat for unowned).
3. Inspect the generated *.c files for the function body:
• Look for g_steal_pointer (or g_object_ref/g_object_unref) around the parameter assignment – present only in the `@owned` version.
• The `@unowned` version should contain a plain assignment without any ref‑count calls.
4. Run valac --version to confirm the compiler version; if it reports 0.56 or newer, expect the difference; otherwise expect no difference.

Missing diagnostic detail

To give a definitive recommendation for your specific setup, please confirm the exact Vala version you are using (output of valac --version).