Re: [boost] [outcome] Possible extensions/changes to std::experimental::expected

2017-05-26 13:12 GMT+02:00 Peter Dimov via Boost :

Peter Dimov wrote:

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Andrzej Krzemienski wrote:

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Also, they way I look at this solution is not "when I get this value I have to check ...", but "when I produce this value I have to make > sure...". Is there no way to acheive this in the language?

By not providing a default constructor, I suppose. Otherwise not, there's return value elision so if you do

result<T> function() { result<T> r;

// do things

return r; }

nothing is ever called on 'r' on your side if you forget to initialize it.

Actually, there is a way, by providing two types, one default-constructible with a singular empty state, one without. In the code above, you will still declare the function to return result<>, which can never be empty and has no default constructor, but declare `r` to be of type result_option, or optional_result, or optional<result>, or whatever. Then the `return r` line will convert and check.

(Or you could use `result r` and return `r.value()`, which is a funny exercise in ambiguity.)

Nice. On the other hand, maybe the solution to this should come in the form of clever, programmer-assisted, static analysis. Regards, &rzej;