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POstd::packaged_task compile error w/ gcc 4.6
 

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  1. POstd::packaged_task compile error w/ gcc 4.6
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    <p>I'm trying to launch a function in a thread using <code>std::packaged_task</code> </p> <pre><code>Query query; /* protobuf object */ /* fill Query object */ std::packaged_task&lt;SearchResults(Query&amp;)&gt; task([](Query&amp; q) -&gt;SearchResults { index::core::Merger merger; return merger.search(q); }); std::future&lt;SearchResults&gt; ftr = task.get_future(); std::thread(std::move(task),query).detach(); </code></pre> <p>Edit2: Updated the code again to fix errors and included the full error message.</p> <p>g++-4.6 (on Ubuntu 10.04) is unable to compile the code: </p> <pre><code>In file included from /usr/include/c++/4.6/memory:80:0, from ../src/net/QueryConnection.cpp:8: /usr/include/c++/4.6/functional: In instantiation of ‘std::_Bind_result&lt;void, std::packaged_task&lt;SearchResults(Query&amp;)&gt;(Query)&gt;’: /usr/include/c++/4.6/thread:135:9: instantiated from ‘std::thread::thread(_Callable&amp;&amp;, _Args&amp;&amp; ...) [with _Callable = std::packaged_task&lt;SearchResults(Query&amp;)&gt;, _Args = {Query&amp;}]’ ../src/net/QueryConnection.cpp:77:36: instantiated from here /usr/include/c++/4.6/functional:1365:7: error: ‘std::_Bind_result&lt;_Result, _Functor(_Bound_args ...)&gt;::_Bind_result(const std::_Bind_result&lt;_Result, _Functor(_Bound_args ...)&gt;&amp;) [with _Result = void, _Functor = std::packaged_task&lt;SearchResults(Query&amp;)&gt;, _Bound_args = {Query}, std::_Bind_result&lt;_Result, _Functor(_Bound_args ...)&gt; = std::_Bind_result&lt;void, std::packaged_task&lt;SearchResults(Query&amp;)&gt;(Query)&gt;]’ declared to take const reference, but implicit declaration would take non-const Build error occurred, build is stopped </code></pre> <p>I've read that this is maybe due to a bug: <a href="http://www.mailinglistarchive.com/html/gcc-help@gcc.gnu.org/2011-11/msg00090.html" rel="nofollow">gcc-mailinglist</a></p> <p>I'm new to C++ / C++11 - What would be a good working alternative? I just need to launch a thread that gives me a future, whom <code>get()</code>-method is called later in an <code>boost::asio</code> async loop. </p>
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    1. COOne problem is that you've declared the packaged_task as taking no arguments and returning a SearchResults, but the lambda takes a single argument. I would expect your declaration to be `std::packaged_task<SearchResults(Query&)>`
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    2. COCan you actually post the full error message? It seems you posted only half of it. That makes it unintelligible.
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    3. COI've changed the code to reflect the missing argument and added the full error message with the updated code. Still lot's of problem.
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