P2561 R2 A control flow operator

[wg21bot]

P2561R0 operator?? (Barry Revzin)

[SavenkovIgor]

Automatic error up propagation is obviously good deed, but in proposed variant it breaks implicit assumptions about ?? operator.

In all languages (which also was mentioned in paper) syntax for ?? operator used like this:
<smth._nullish> ?? <default_value>;
but not like this:
<smth. nullish>??; // implicitly return error if something bad happens

I think that ?. and ?? operators (if they would appear in c++), must be used in exactly same syntax and meaning as in all other languages. ?. - for optional access if not null, ?? is for finalizing nullish expression

Maybe something like "guard let" syntax from Swift would suit here better?

// in Swift it looks like this:
guard let item = inventory[name] else {
            return indexOutOfBounds
}
print(item)
// item is unwrapped and visible after guard operator, opposing to "if (auto x = y)" syntax from c++

[mnaydenov]

It seems to me, this overlaps with co_await way too much. Improving coroutines seems like a better approach instead of inventing a new tool for, effectively, a subset of coroutines.

[flamewing]

@mnaydenov It overlaps with a class of abuses of co_await operator; why should one need to turn a function into a coroutine in order to benefit from this kind of automatic error propagation operator? It would be better to have a proper language feature so this kind of abuse is no longer needed.

Also, adding this as a language feature neither prevents nor hampers the development/improvement of coroutines.

[jwakely]

This GitHub issue is for tracking the procedural/admin status of the paper, not technical discussion of the paper's content. Please use the std proposals forum for discussion.
https://isocpp.org/std/forums

[wg21bot]

P2561R1 An error propagation operator (Barry Revzin)

[erichkeane]

Given our limited resources, EWG would like to see more work in the direction of P2561R1.

SF	F	N	A	SA
8	9	7	1	2

Result: Consensus

[wg21bot]

P2561R2 A control flow operator (Barry Revzin)