Re: [boost] [review] Review of Outcome v2 (Fri-19-Jan to Sun-28-Jan, 2018)

2018-02-03 23:32 GMT+01:00 Rob Stewart via Boost :

That result is declared with [[nodiscard]] can be helpful. It means the return value of a function returning a result cannot be ignored. Unfortunately, the compiler doesn't require that the programmer do anything with the result except save it. (A warning might alert the programmer to do something with such a variable, but there's no enforcement.)

Let me expand on this a bit. I have the following program where I save the result, but not inspect it: ``` #include "outcome.hpp" namespace out = OUTCOME_V2_NAMESPACE; out::result<void> fun() { return out::success(); } int main() { auto r = fun(); } ``` When I compile with clang, with -Wall -Wextra -Werror, I get an error saying, "unused variable 'r'". See online examle: https://wandbox.org/permlink/WE7dK6r5XCIxJ83f When I compile with GCC, I do not get this warning. But in my work, w compile programs with GCC, but still use clang for the static analysis pass, and nonetheless this bug would be detected. Of course, you could still overcome all the safety precautions and trigger an UB: ``` #include "outcome.hpp" namespace out = OUTCOME_V2_NAMESPACE; out::result<void> fun() { return out::success(); } int main() { auto r = fun(); (void)r; } ``` But I would not expect protection from such conscious attempts of overcoming safety measures.

The same is not documented for outcome, however. Thus, when using outcome, because one might need to convey an exception to the caller, there is no compiler help to ensure the programmer doesn't ignore the return value.

When I test the following program, it does tell me that I am not inspecting the returned outcome: ``` #include "outcome.hpp" namespace out = OUTCOME_V2_NAMESPACE; out::outcome<int> fun() { return out::success(1); } int main() { fun(); } ``` So, you probably mean something else than I think. Could you illustrate your concerns with an example? Regards, &rzej;