Boost logo

Boost :

Subject: Re: [boost] [thread] Boost.Thread defines boost::move which conflicts with Boost.Move
From: Evan Wallace (onlyone_at_[hidden])
Date: 2012-01-09 09:07:07

On Thu, 05 Jan 2012 07:00:27 +0100, Vicente J. Botet Escriba wrote:>Mankarse please, could you post here the patch for the boost.thread >class so that I can start the integration of what you have already done? I have attached a patch to the ticket ( This patch is fairly comprehensive in terms of code, but it does not include any tests or documentation. In the course of writing the patch, I created some simple tests, but I have not yet translated these into Boost.Test testcases, or included them in the patch. I have tested the basic functionality on a number of compilers, but there are probably still some bugs in the patched code. The patch contains a number of known problems that may be worth discussing:1) Explicit move() and copy() calls:boost::thread and boost::packaged_task both have templated constructors that take an rvalue reference to a functor (which they move or copy as appropriate). Templates parameters cannot be deduced to a type that is only reachable through an conversion operator. Template constructors can also never be explicitly instansiated. (As far as I know.) This means that the overloads that are used in the definitions of BOOST_COPYABLE_AND_MOVABLE types (BOOST_RV_REF(type), BOOST_CATCH_CONST_RLVALUE(type), type&), are not matched for rvalue objects (in C++03 mode). Example:     //In C++11 the `CopyableAndMovableFunctor` would be    //moved into the thread.    //In C++03 this does not compile.    boost::thread((CopyableAndMovableFunctor())) Here, no overload would be matched, because the `type` in the overloads is templated. To solve this problem I modified Boost.Move to add two member functions - `copy()` and `move()` - which forward to the rv const& and rv& conversion operators. With these, the above example can be rewritten as:     //In both C++11 and C++03 the `CopyableAndMovableFunctor`    //will be moved or copied into the thread as appropriate.    boost::thread(CopyableAndMovableFunctor().move()),    boost::thread(CopyableAndMovableFunctor().copy()) I can imagine the names `copy` and `move` being quite common, so this might cause unfortunate conflicts. Is this an acceptable change to Boost.Move? Is there another way to get the functionality that does not require this? 2) SFINAE requiredBoost.Move requires SFINAE, and by extension Boost.Thread now also requires SFINAE. Previously, Boost.Thread did not require SFINAE. Is this an acceptable regression, or should more work be put into maintaining compatibility with compilers that do not support SFINAE? 3) Not using has_move_emulation_enabledI did not notice the `has_move_emulation_enabled` metafunction, and instead used `is_convertible!(T&, boost::rv!(T))`. This may mean that some situations that `has_move_emulation_enabled` accounts for will not be accounted for by the code in the patch. I have not yet evaluated whether simply replacing all the occurrences will work. Any thoughts? 4) Not using Vicente's patches for #6174 or #5990By the time that I was aware of these patches, I had already independently fixed the issues. I have not looked at either patch in detail, but they each go about fixing the issues in a significantly different way from my patch. Which code should be used in each of these cases? Where should I go from here? I could do the integration into the svn trunk version, write the documentation, or update the tests to the new version. Are there any other tasks that I can help out with? I will of course keep the patch updated with fixes for any bugs that I find in it. Evan Wallace

Boost list run by bdawes at, gregod at, cpdaniel at, john at