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RFC: .. in patterns#1492

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petrochenkov:patdotdot
May 13, 2016
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RFC: .. in patterns#1492
nikomatsakis merged 2 commits intorust-lang:masterfrom
petrochenkov:patdotdot

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@petrochenkov petrochenkov commented Feb 6, 2016

Permit the .. pattern fragment in more contexts.

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petrochenkov commented Feb 6, 2016

cc rust-lang/rust#31443

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text/0000-dotdot-in-patterns.md
[unresolved]: #unresolved-questions

Sublist binding syntax conflicts with possible exclusive range patterns
`begin .. end`/`begin..`/`..end`. This problem already exists for slice patterns and has to be
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Slice patterns are unstable (and buggy), and thus can easily be changed.

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Extensions proposed in this RFC are going to be unstable too and are supposed to be changed together with slice patterns if changed at all.

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oli-obk commented Feb 8, 2016

Should S(a, b, ..) be allowed for struct S(A, B); ? For structs it currently is: http://is.gd/TsMz6N .

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petrochenkov commented Feb 8, 2016

Should S(a, b, ..) be allowed for struct S(A, B); ?

Yes, .. means 0 or more subpatterns.

@nrc nrc added the T-lang Relevant to the language team, which will review and decide on the RFC. label Feb 8, 2016
@aturon aturon self-assigned this Feb 11, 2016
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nikomatsakis commented Feb 11, 2016

This was pretty Always The Plan -- but we never did it because it involved work. I'm basically 👍 though I've not read the details of the RFC.

@petrochenkov petrochenkov mentioned this pull request Feb 15, 2016
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bors added a commit to rust-lang/rust that referenced this pull request Feb 17, 2016
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Auto merge of #31685 - petrochenkov:patrefact2, r=eddyb
0d1cd9b 
And split `PatKind::Enum` into `PatKind::TupleStruct` and `PatKind::Path`.
This is the HIR part of #31581.
This is also kind of a preparation for rust-lang/rfcs#1492.

r? @eddyb
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petrochenkov commented Mar 6, 2016

Implementation (without sub-list bindings): rust-lang/rust#32079

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nikomatsakis commented Apr 12, 2016

Nominating for FCP.

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petrochenkov commented Apr 27, 2016

I should probably strike out the sub-tuple bindings (a, b, c..) from this RFC given the discussion in #1582 and #376, at least for now.

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nikomatsakis commented May 2, 2016

Hear ye, hear ye! This RFC is now entering final comment period.

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nikomatsakis commented May 2, 2016

@petrochenkov very well... to be honest I've not read this closely, though I'm in favor of the spirit. We had decided to put this into FCP, but would you rather we wait? (We can keep your proposed edit in mind, I imagine.)

@nikomatsakis nikomatsakis added final-comment-period Will be merged/postponed/closed in ~10 calendar days unless new substational objections are raised. and removed I-nominated labels May 2, 2016
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text/0000-dotdot-in-patterns.md
[subpat1, .., subpatN]
// Slice patterns, any of the above with a subslice binding.
// By ref bindings are allowed, slices and subslices always have compatible layouts.
[subpat1, binding.., subpatN]
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What does this binding mean? This feels like it overlaps with slice patterns, which (I think) still require some further RFC to "complete"? I can't remember if we postponed that work or not. :)

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What does this binding mean?

A subslice pattern, see above - "The binding is not actually a binding, but one more pattern ..."

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nikomatsakis commented May 12, 2016

I'd be (more) in favor of a variant of this that excludes all "bindings". In other words, allowing:

(pat*, .., pat*)
Foo(pat*, .., pat*)

and I'd probably prefer to exclude [] patterns which I think ought to be handled separately.

The binding forms introduce complicated semantics.

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petrochenkov commented May 12, 2016

@nikomatsakis

I'd probably prefer to exclude [] patterns

This RFC doesn't propose any changes to slice patterns, it only uses them for analogy.

I'd be (more) in favor of a variant of this that excludes all "bindings".

With this I agree.

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nikomatsakis commented May 12, 2016

@petrochenkov

This RFC doesn't propose any changes to slice patterns, it only uses them for analogy.

Huh. OK, I must have misread it. So much the better.

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brendanzab commented May 12, 2016

I missed that subtlety too - maybe removing the slice examples might make it clearer?

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nikomatsakis commented May 13, 2016

Huzzah! The @rust-lang/lang team has decided to accept this RFC. Specifically:

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nikomatsakis commented May 13, 2016

Tracking issue: rust-lang/rust#33627

If you'd like to keep following the development of this feature, please subscribe to that issue, thanks! :)

@nikomatsakis nikomatsakis merged commit 4e9e843 into rust-lang:master May 13, 2016
@Stebalien Stebalien mentioned this pull request Aug 19, 2016
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@petrochenkov petrochenkov deleted the patdotdot branch September 21, 2016 20:28
critiqjo pushed a commit to critiqjo/rustdoc that referenced this pull request Dec 16, 2016
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Auto merge of #31685 - petrochenkov:patrefact2, r=eddyb
13dcd0c 
And split `PatKind::Enum` into `PatKind::TupleStruct` and `PatKind::Path`.
This is the HIR part of rust-lang/rust#31581.
This is also kind of a preparation for rust-lang/rfcs#1492.

r? @eddyb
@Centril Centril added A-syntax Syntax related proposals & ideas A-patterns Pattern matching related proposals & ideas A-data-types RFCs about data-types A-tuples Proposals relating to tuples. A-slice Slice related proposals & ideas labels Nov 23, 2018
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A-data-types RFCs about data-types A-patterns Pattern matching related proposals & ideas A-slice Slice related proposals & ideas A-syntax Syntax related proposals & ideas A-tuples Proposals relating to tuples. final-comment-period Will be merged/postponed/closed in ~10 calendar days unless new substational objections are raised. T-lang Relevant to the language team, which will review and decide on the RFC.

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