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P1371 Pattern Matching #166

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jensmaurer opened this issue Jan 26, 2019 · 19 comments
Open

P1371 Pattern Matching #166

jensmaurer opened this issue Jan 26, 2019 · 19 comments
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EWG Evolution needs-revision Paper needs changes before it can proceed

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@jensmaurer
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jensmaurer commented Jan 26, 2019

P1371R0 Pattern Matching (Sergei Murzin, Michael Park, David Sankel, Dan Sarginson)

@jensmaurer jensmaurer added this to the 2019-02 milestone Jan 26, 2019
@jensmaurer jensmaurer added the EWG Evolution label Jan 26, 2019
@villevoutilainen villevoutilainen added this to EWGSaturday in EWGKonaFeb2019 Feb 11, 2019
@jfbastien
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jfbastien commented Feb 12, 2019

P1260R0 Pattern Matching #363 and P1308R0 Pattern Matching #364 were seen by EWGI in SAN.
Strong support, authors got feedback to address.

@jensmaurer
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jensmaurer commented Mar 20, 2019

EWG in Kona

@jensmaurer jensmaurer removed this from the 2019-02 milestone Mar 20, 2019
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wg21bot commented Jun 23, 2019

P1371R1 Pattern Matching (Sergei Murzin, Michael Park, David Sankel, Dan Sarginson)

@wg21bot wg21bot added this to the 2019-07 milestone Jun 23, 2019
This was referenced Jul 8, 2019
@jensmaurer
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jensmaurer commented Aug 23, 2019

EWG in Cologne

@jensmaurer jensmaurer removed this from the 2019-07 milestone Aug 23, 2019
@jfbastien jfbastien added this to Would be nice to talk about in EWGBelfast2019 Oct 15, 2019
@jfbastien jfbastien moved this from Would be nice to talk about to Wednesday in EWGBelfast2019 Nov 5, 2019
@jfbastien
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jfbastien commented Nov 7, 2019

EWG saw this: http://wiki.edg.com/bin/view/Wg21belfast/P1371-EWG

EWG is interested in hearing more about pattern matching in the general direction presented

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wg21bot commented Jan 18, 2020

P1371R2 Pattern Matching (Sergei Murzin, Michael Park, David Sankel, Dan Sarginson)

@wg21bot wg21bot added this to the 2020-02 milestone Jan 18, 2020
@jfbastien jfbastien added this to Unscheduled in EWG Prague Jan 22, 2020
@jfbastien jfbastien moved this from Unscheduled to Tuesday in EWG Prague Jan 23, 2020
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jfbastien commented Feb 11, 2020

EWG Prague on Tuesday afternoon:

Pattern matching should require a case that always matches.

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Assuming we don’t mandate a case that always matches, if no case matched, we get UB.

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Drop the expression form.

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Drop the statement form.

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Pattern matching shouldn’t have arbitrary lookahead.

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31 10 3 1 0

@jfbastien jfbastien added the needs-revision Paper needs changes before it can proceed label Feb 11, 2020
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jfbastien commented Feb 14, 2020

EWG Prague Friday afternoon, discuss design tuning: an update from earlier this week, Pattern_Matching_Updates.pdf

Non-void inspect expressions should have at least one pattern which, on its own, can match every possible value.

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0 0 2 11 13

@jensmaurer jensmaurer removed this from the 2020-02 milestone Feb 18, 2020
@jfbastien
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jfbastien commented Aug 27, 2020

We discussed exhaustiveness checking in today's EWG telecon, and took the following poll:

POLL We like the presented approach to exhaustiveness checking in pattern matching.

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6 11 5 2 1

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jfbastien commented Sep 16, 2020

EWG discussed "inspect is always an expression" in a telecon today.

POLL: Allow break and continue leaving from inspect expressions.

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Lots of other feedback was given to the authors, and everyone agreed to more exploration. We did not poll these.

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wg21bot commented Sep 23, 2020

P1371R3 Pattern Matching (Michael Park, Bruno Cardoso Lopes, Sergei Murzin, David Sankel, Dan Sarginson, Bjarne Stroustrup)

@wg21bot wg21bot removed the needs-revision Paper needs changes before it can proceed label Sep 23, 2020
@wg21bot wg21bot added this to the 2020-telecon milestone Sep 23, 2020
@jfbastien
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jfbastien commented Nov 19, 2020

Today in the EWG telecon, we discussed goto in pattern actions. Polls:

Support goto jumping into a pattern.

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0 0 1 4 19

Support goto jumping out of a pattern, when the goto jumps forward, not across a variable declaration or into a nested scope.

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1 12 6 3 1

Support goto jumping out of a pattern, without additional constraints.

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2 3 11 5 1

Support goto which remains strictly within its pattern.

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7 8 6 0 0

Bjarne wrote a short paper to start our discussion, and will come back with a bigger paper which covers all the cases and feedback received.

@jensmaurer jensmaurer modified the milestones: 2020-telecon, 2021-telecon Dec 28, 2020
@jfbastien
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jfbastien commented Mar 2, 2021

Bruno presented his implementation experience to EWG on 2021-02-25.
Godbolt demo: https://godbolt.org/z/fdd5j4
Feedback was given to the authors.

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jfbastien commented Apr 15, 2021

EWG discussed Pattern matching identifier patterns syntax: let vs auto vs none on April 8th.

POLL: annotate id-pattern with auto.

inspect (e) { // like this:
 
  auto&& x => binds

  x => matches

}
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POLL: if we annotate id-patterns with let.

inspect (e) { // like this:

  let x => binds

  x => matches

}
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POLL: keep the current p1371r3 proposal with case.

inspect (e) { // like this:

  x => // binds

  case x => matches

}
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2 6 8 0 3

@jensmaurer jensmaurer modified the milestones: 2021-telecon, 2022-telecon Jan 1, 2022
@erichkeane erichkeane added the needs-revision Paper needs changes before it can proceed label Mar 7, 2022
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erichkeane commented Mar 7, 2022

Adding needs-revision, this got EWG feedback in April of '21.

@jensmaurer jensmaurer removed this from the 2022-telecon milestone Mar 7, 2022
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