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POCan std::async be use with template functions
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10620300
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10620923
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2
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1
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2012-05-16T14:07:21.063
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2017-06-26T16:44:40.553
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2012-05-16T14:10:53.303
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Is <a href="http://en.cppreference.com/w/cpp/thread/async"><code>std::async</code></a> supose to work with template function? I've tried to lauch <a href="http://en.cppreference.com/w/cpp/algorithm/reverse"><code>std::reverse</code></a> as an asynchronous task bu got compile-time error. I've tried to use simpler functions (foo and bar) and discover that only the non-template-function are working. <pre><code>#include <algorithm> #include <future> #include <string> void foo(std::string::iterator first, std::string::iterator last) { } template<class BidirectionalIterator> void bar(BidirectionalIterator first, BidirectionalIterator last) { } int main() { std::string str = "Lorem ipsum, dolor sit amet"; auto result_reverse = std::async(std::reverse, str.begin(), str.end()); // Compile-time error auto result_foo = std::async(foo, str.begin(), str.end()); auto result_bar = std::async(bar, str.begin(), str.end()); // Compile-time error result_reverse.get(); result_foo.get(); result_bar.get(); } </code></pre> The compiler error is as follow: <pre><code>main.cpp: In function ‘int main()’: main.cpp:18:71: erreur: no matching function for call to ‘async(<unresolved overloaded function type>, std::basic_string<char>::iterator, std::basic_string<char>::iterator)’ main.cpp:18:71: note: candidates are: /usr/include/c++/4.6/future:1355:5: note: template<class _Fn, class ... _Args> std::future<typename std::result_of<_Functor(_ArgTypes ...)>::type> std::async(std::launch, _Fn&&, _Args&& ...) /usr/include/c++/4.6/future:1378:5: note: template<class _Fn, class ... _Args> typename std::__async_sfinae_helper<typename std::decay<_Functor>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...) main.cpp:18:71: erreur: unable to deduce ‘auto’ from ‘<expression error>’ main.cpp:20:62: erreur: no matching function for call to ‘async(<unresolved overloaded function type>, std::basic_string<char>::iterator, std::basic_string<char>::iterator)’ main.cpp:20:62: note: candidates are: /usr/include/c++/4.6/future:1355:5: note: template<class _Fn, class ... _Args> std::future<typename std::result_of<_Functor(_ArgTypes ...)>::type> std::async(std::launch, _Fn&&, _Args&& ...) /usr/include/c++/4.6/future:1378:5: note: template<class _Fn, class ... _Args> typename std::__async_sfinae_helper<typename std::decay<_Functor>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...) main.cpp:20:62: erreur: unable to deduce ‘auto’ from ‘<expression error>’ </code></pre> However, it pass when I manually specify the template instanciation, such as <code>std::async(std::reverse<std::string::iterator>, str.begin(), str.end())</code>. Is this a compiler bug (GCC 4.6.3) or a well defined behaviour?
Tags
<c++><templates><asynchronous><c++11><std>
Title
Can std::async be use with template functions
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1. PO
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1. USauthchir
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1. PO
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2. VO
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1. COTemplates aren't functions, so the behaviour is correct according to the standard. If you want deduced arguments, you need to wrap it in a functor.
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