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Smarter integration of projection predicates into trait selection #20297

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nikomatsakis opened this issue Dec 29, 2014 · 4 comments
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Smarter integration of projection predicates into trait selection #20297

nikomatsakis opened this issue Dec 29, 2014 · 4 comments
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A-trait-system Area: Trait system A-type-system Area: Type system

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@nikomatsakis
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The current logic that integrates projection predicates into trait selection is somewhat flawed. I made some simplifying choices:

  1. For one thing, it only works if the self type is a projection type, but in reality it should be able to handle any input type. Moreover, there may be multiple projection types in play.
  2. Also, the integration with inference is not particularly smart.
  3. Finally, if there are where clauses that overlap with projections, we currently just choose the where clause every time, but this may influence inference or have other subtle effects.

These all feel a bit like corner cases for now and I think we can get away with leaving things as they are and later coming in with a much smarter trait selection system. It's clear that we're pushing the bounds of the current setup. Trait reform 2.0 anybody?
@kmcallister kmcallister added A-trait-system Area: Trait system A-type-system Area: Type system labels Jan 16, 2015
@edwardw edwardw mentioned this issue Jan 30, 2015
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@jroesch
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jroesch commented Feb 7, 2015

cc me

arielb1 referenced this issue in arielb1/rust Mar 17, 2015
@arielb1
Select projections over impls in case of ambiguity. Fixes rust-lang#2…
eeace7c 
…3336.
@tamird tamird mentioned this issue May 12, 2015
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@nikomatsakis nikomatsakis mentioned this issue Nov 2, 2015
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@steveklabnik
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Triage: no idea what's going on with this, and it's very, very old. @nikomatsakis is this still relevant?

@Mark-Simulacrum
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Is this still relevant? It's a very old issue, and it seems there was some progress judging by the items in GH's log.

@nikomatsakis
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This is all still relevant but I feel this issue adds approximately zero value. Closing.

@nikomatsakis nikomatsakis mentioned this issue May 25, 2017
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@oli-obk oli-obk mentioned this issue Sep 6, 2017
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nivkner added a commit to nivkner/rust that referenced this issue Oct 7, 2017
@nivkner
address more FIXME whose associated issues were marked as closed
e0ac65e 
update FIXME(rust-lang#6298) to point to open issue 15020
update FIXME(rust-lang#6268) to point to RFC 811
update FIXME(rust-lang#10520) to point to RFC 1751
remove FIXME for emscripten issue 4563 and include target in `test_estimate_scaling_factor`
remove FIXME(rust-lang#18207) since node_id isn't used for `ref` pattern analysis
remove FIXME(rust-lang#6308) since DST was implemented in rust-lang#12938
remove FIXME(rust-lang#2658) since it was decided to not reorganize module
remove FIXME(rust-lang#20590) since it was decided to stay conservative with projection types
remove FIXME(rust-lang#20297) since it was decided that solving the issue is unnecessary
remove FIXME(rust-lang#27086) since closures do correspond to structs now
remove FIXME(rust-lang#13846) and enable `function_sections` for windows
remove mention of rust-lang#22079 in FIXME(rust-lang#22079) since this is a general FIXME
remove FIXME(rust-lang#5074) since the restriction on borrow were lifted
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@steveklabnik @nikomatsakis @kmcallister @jroesch @Mark-Simulacrum