On Wed, 8 Aug 2012, François Dumont wrote:
On 08/08/2012 09:34 AM, Marc Glisse wrote:
On Tue, 7 Aug 2012, Richard Smith wrote:
I've attached a patch for unordered_map which solves the rvalue
reference problem. For efficiency, I've created a new
_M_emplace_bucket method rather than call emplace directly.
I've verified all libstdc++ tests pass (sorry for the previous
oversight) and am running the full GCC test suite now. However, I'd
appreciate any feedback on whether this is a reasonable approach. STL
hacking is way outside my comfort zone. ;-)
If this looks good, I'll take a stab at std::map.
I think you should remove the mapped_type() argument from the call to
_M_emplace_bucket. In C++11, the mapped_type is not required to be
copyable
at all, just to be DefaultInsertable.
Indeed. The reason I was talking about emplace is that you want an object
to be created only at the time the node is created. That might mean passing
piecewise_construct_t and an empty tuple to emplace (otherwise it is too
similar to insert). Or for unordered_map where the node functions are
"exposed", you could just create the node directly without passing through
emplace.
This is what I try to do in the attached patch. I replace _M_insert_bucket
with _M_insert_node and use it for operator[] implementation. I have also
introduce a special std::pair constructor for container usage so that we do
not have to include the whole tuple stuff just for associative container
implementations.
However one test is failing:
/home/fdt/dev/gcc/libstdc++-v3/testsuite/23_containers/unordered_map/insert/array_syntax_move.cc:39:18:
required from here
/home/fdt/dev/gcc-build/x86_64-unknown-linux-gnu/libstdc++-v3/include/bits/stl_pair.h:175:42:
error: use of deleted function '__gnu_test::rvalstruct::rvalstruct(const
__gnu_test::rvalstruct&)'
: first(std::forward<_T1>(__x)), second() { }
I don't understand why it doesn't use the move constructor. I can't see any
std::forward call missing. Anyone ?
You are dealing with a pair<T1,T2> where T1 is const T3.
It is roughly the same issue as before, we end up trying to call a move
constructor on a const&&.
You probably want your pair constructor to accept T3&&, not T1&&.
--
Marc Glisse
