Re: [boost] [optional] Suggestion for adding an optional_number class

On 21.07.2017 10:47, Viktor Sehr via Boost wrote:

I'd like to make a suggestion for adding an optional class for number types, called optional_number, where the max value of the number type is utilized as the uninitalized value.

Differences compared to std::optional: *- No size overhead from the wrapped type* - Theoretically faster (althrough in practice probably negilble) - Can be assigned to any value except the max value - Operator-> is removed as it does not make sense for an integer

Notes: - Throws if assigned the numeric_limits<T>::max - Also works with enums, using the underlying_type - The operator bool conversion is missing in the prototype implementation

Attaching a prototype implementation (currently for C++14).

/Viktor

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Hello, FYI there was a proposal recently for optional with the same purpose; unfortunately, it went nowhere: https://lists.boost.org/Archives/boost/2015/09/225692.php Though I think that a most valuable rationale for it is this special optional being a tool for wrapping legacy code or systems that already utilize special value idiom. Also, throw on special value assignment is insane - it might be perfectly fine to pass special values to indicate something other than error - say, in a system it might be defined as a missing value (e.g. NaN meaning n/a). Or a completely different thing - special value as a non-error, everything else as an error; it may add usability to thin wrappers to legacy API. -------- Mitsyn Sergey