{"ast_node_type":"other","tokens":[{"end":66,"kind":"keyword","start":0,"text":"match"}]}
                match (src_tty.principal(), dst_tty.principal()) {
            (PointerKind::VTable(src_tty), PointerKind::VTable(dst_tty)) => {
                    // A<dyn Src<...> + SrcAuto> -> B<dyn Dst<...> + DstAuto>. need to make sure