On 31/05/2017 17:42, Vicente J. Botet Escriba wrote:
Le 31/05/2017 à 12:55, Niall Douglas via Boost a écrit :
I guess, ultimately, the question to be answered here is how much like std::variant<...> should Outcome and/or Expected be? std::variant<...> doesn't implement completely unchecked observers like optional's operator*(), the best you can get is a nulled pointer observer, no silent reinterpret_cast.
When I started the Expected proposal Variant was not yet there. I believe that we could add the following from variant: * visit * index * get_if/value_if * get
Apart from the lack of never empty guarantee (which can be worked around), there appears to be no good reason to not use std::variant<T, E> to implement std::expected<T, E>. Well, apart from poor quality of implementation of std::variant sometimes. For example, libstdc++'s for GCC 7.1 appears to always use type erased memory allocation. Which, frankly, is daft in C++ 14 when you are storing either an int or a std::error_code. I would also assume that std::bad_alloc can be thrown from libstdc++'s std::variant<> :( (Dinkumware's std::variant<...> is really nice, optimises beautifully with an all-trivial-when-possible implementation, well done on them) Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/