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1273.future::valid should be callable on an invalid future

Section: 32.10.7[futures.unique.future]Status:ResolvedSubmitter: Jonathan WakelyOpened: 2009-11-22Last modified: 2021-06-06

Priority:Not Prioritized

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Discussion:

[futures.unique_future]/3 says:

The effect of calling any member function other than the destructor orthe move-assignment operator on afuture object for whichvalid() == false is undefined.

This means callingfuture::valid() is undefined unless it willreturntrue, so you can only use it if you know the answer!

[2009-12-08 Moved to Tentatively Ready after 5 positive votes on c++std-lib.]

[2010 Pittsburgh:]

Moved toNAD EditorialResolved. Rationale added below.

Rationale:

Solved byN3058.

Proposed resolution:

Change [futures.unique_future]/3:

The effect of calling any member function other than thedestructor, or the move-assignment operator, orvalid, on afuture object for whichvalid()== false is undefined.