Sorry for that, I've made in implementation with free functions which compiles on VS 2012: #include <assert.h> #include <boost/optional.hpp> template<class T, class B> auto bind(const boost::optional<T>& optional, B&& binder) -> typename std::decay<decltype(std::bind(binder, *optional)())>::type { if(optional) { return std::bind(binder, *optional)(); } else { return boost::none; } } template<class T, class B> auto map(const boost::optional<T>& optional, B&& binder) -> boost::optional<typename std::decay<decltype(std::bind(binder, *optional)())>::type> { if(optional) { return std::bind(binder, *optional)(); } else { return boost::none; } } void foo() { struct A { int i; }; boost::optional<A> opt_a; auto opt_i = map(opt_a, &A::i); assert(!opt_i); A a = {42}; opt_a = a; auto opt_i2 = map(opt_a, &A::i); assert(*opt_i2 == 42); } Von: Andrzej Krzemienski [via Boost] [mailto:ml-node+s2283326n4677432h98@n4.nabble.com] Gesendet: Montag, 22. Juni 2015 16:02 An: Löw, Tobias (STEAG Energy Services GmbH) Betreff: Re: [Optional] Monadic bind 2015-06-22 15:49 GMT+02:00 Tobias Loew <[hidden email]</user/SendEmail.jtp?type=node&node=4677432&i=0>>:
While playing around with boost::optionals I had code like the following
struct A { ... int i; ... };
boost::optional a; // do something with 'a'
// optional-projection to a::i boost::optional<int> a_i; if(a) a_i = a->i;
Could you give us an example here that would compile? boost::optional a; The above is not a valid variable declaration (template argument missing), so it is difficult for me to gather what you are trying to do. Regards, &rzej _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost ________________________________ If you reply to this email, your message will be added to the discussion below: http://boost.2283326.n4.nabble.com/Optional-Monadic-bind-tp4677431p4677432.h... To unsubscribe from [Optional] Monadic bind, click here<http://boost.2283326.n4.nabble.com/template/NamlServlet.jtp?macro=unsubscribe_by_code&node=4677431&code=VG9iaWFzLkxvZXdAc3RlYWcuY29tfDQ2Nzc0MzF8MTI1MDAzMDE5Mg==>. NAML<http://boost.2283326.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml> -- View this message in context: http://boost.2283326.n4.nabble.com/Optional-Monadic-bind-tp4677431p4677434.h... Sent from the Boost - Dev mailing list archive at Nabble.com.