Implementing an abstract construct property in a different file from the one in which it is originally declared is not possible.

Example:

$ cat proptest_iface.vala
public interface HasProperty : Object
{
    public abstract string myprop { get; construct; }
}

$ cat proptest_impl.vala
public abstract class ImplementsProperty  : Object, HasProperty
{
    public string myprop { get; construct; }
}

void main ()
{
}

$ valac-0.18 proptest_iface.vala proptest_impl.vala
/home/tjol/tmp/proptest_impl.vala.c:65:13: warning: ‘has_property_set_myprop’ used but never defined [enabled by default]
/tmp/ccCogCi2.o: In function `_vala_implements_property_set_property':
proptest_impl.vala.c:(.text+0x42a): undefined reference to `has_property_set_myprop'
collect2: ld returned 1 exit status
error: cc exited with status 256
Compilation failed: 1 error(s), 0 warning(s)



The reason for this is that the generated set method is static, which makes sense when the property declaration and constructor definition are in the same source file. For abstract properties, this can't be counted on.

static void has_property_set_myprop (HasProperty* self, const gchar* value);