Postconditions vs. exceptions
Jens Maurer

Created on 2012-03-08.00:00:00 last changed 15 months ago


Date: 2021-06-15.00:00:00

[ 2021-06-20; Daniel comments ]

An informal editorial change suggestion has recently been made whose editorial implementation would promote the idea that the default assumption is that Postconditions: are only met if the function doesn't exit with an exception.

After analyzing all current existing Postconditions: elements the following seems to hold: Affected by this issue are only non-noexcept functions and mostly non-constructor functions (unless the Postconditions: element says something about the value of its arguments). Most existing Postconditions seem to be intended to apply only in non-exceptional cases. I found some where this is presumably not intended, namely those of the expressions os << x and is >> v in Tables [tab:rand.req.eng] and [tab:rand.req.dist], maybe also [time.zone.db.remote] p4.

Nonetheless, the editorial change seems to be applicable even without having this issue resolved, because it doesn't actually change the normative state by itself.

Date: 2015-05-06.00:00:00

[ 2015-05-06 Lenexa: EirkWF to write paper addressing 2136 and 2137 ]

MC: Idea is to replace all such "If no exception" postconditions with "Exception safety" sections.

Date: 2012-10-16.15:35:12

[ 2012-10 Portland: Move to Open ]

Consensus that we do not clearly say this, and that we probably should. A likely location to describe the guarantees of postconditions could well be a new sub-clause following [res.on.required] which serves the same purpose for requires clauses. However, we need such wording before we can make progress.

Also, see 2137 for a suggestion that we want to see a paper resolving both issues together.

Date: 2012-03-08.00:00:00

The front matter in clause 17 should clarify that postconditions will not hold if a standard library function exits via an exception. Postconditions or guarantees that apply when an exception is thrown (beyond the basic guarantee) are described in an "Exception safety" section.

Date User Action Args
2021-06-20 15:08:44adminsetmessages: + msg11948
2015-05-22 19:00:31adminsetmessages: + msg7424
2012-10-16 15:35:12adminsetmessages: + msg6168
2012-10-16 15:35:12adminsetstatus: new -> open
2012-03-08 00:00:00admincreate