2014-06-28 23:52 GMT+02:00 Krzysztof Czainski <1czajnik@gmail.com>:
2014-06-28 22:58 GMT+02:00 Andrzej Krzemienski <akrzemi1@gmail.com>:
Hi, This is the second time that I have found the following function useful when playing with variants of Optional library:
template <typename T, typename U> typename std::enable_if<std::is_convertible<U, T>::value, T>::type convert(U && u) { return std::forward<U>(u); }
It performs an implicit conversion from U to T, but you can call it explicitly.
+1
I even have such a function in my tools, and use it often.
I chose a shorter name "as", because since this only forces an implicit conversion, I find verbosity unwanted here.
Consider preventing dangerous uses like this (not tested): auto& x = convert<T const&>( U() );
You can prevent that by adding a static_assert in this function: // Prevent returning an lvalue reference to a temporary BOOST_STATIC_ASSERT( !is_lvalue_reference<T>::value || is_reference<U>::value );
BTW, why not get rid of the enable_if< is_convertible > part? Won't a message "U isn't convertible to T" pointing into the function be more readable, than a message "There's no 'convert' function"?
If I remove enable_if, my second use cans will stop working -- because the semantics of convert() are no longer visible to sfinae. Regards, &rzej