Macro interface_decl 

macro_rules! interface_decl {
    (
        unsafe trait $name:ident ( $vtbl:ident, $impl_trait:ident ) : $parent:ty = $iid:literal {
            $($methods:tt)*
        }
    ) => { ... };
}

Declares a COM interface inheriting from IUnknown, without using the #[interface] proc-macro.