DST coercions #24619
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DST coercions #24619
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Should this be cherry-picked into 1.0? |
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@brson I think no: it is a feature, not a fix, and it is large and thus potentially dangerous bug-wise. I think it is fine to wait an extra 6 weeks for. |
Hmm, not 3 weeks from now? |
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☔ The latest upstream changes (presumably #24674) made this pull request unmergeable. Please resolve the merge conflicts. |
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This is awesome to see! I agree that it may be too late into the cycle to accept something this major into 1.0, but just for the heck of it do we know of any stdlib APIs that require unnecessarily-boxed trait objects that would benefit from this change? |
ftxqxd
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This + DST coercions (rust-lang#24619) would allow code like `Rc<RefCell<Box<Trait>>>` to be simplified to `Rc<RefCell<Trait>>`.
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This + DST coercions (#24619) would allow code like `Rc<RefCell<Box<Trait>>>` to be simplified to `Rc<RefCell<Trait>>`.
ftxqxd
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This + DST coercions (rust-lang#24619) would allow code like `Rc<RefCell<Box<Trait>>>` to be simplified to `Rc<RefCell<Trait>>`.
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@nrc sorry for the delay. I'm going to try and finish this review today. I've been wanting to dig specifically into the question of higher-ranked bounds and the use of |
ftxqxd
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This + DST coercions (rust-lang#24619) would allow code like `Rc<RefCell<Box<Trait>>>` to be simplified to `Rc<RefCell<Trait>>`.
bors
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May 3, 2015
This + DST coercions (#24619) would allow code like `Rc<RefCell<Box<Trait>>>` to be simplified to `Rc<RefCell<Trait>>`.
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How does this impact stable APIs? Is there any way we can merge it and let mature and not insta-stabilize? |
+ lots of rebasing
* segfault due to not copying drop flag when coercing * fat pointer casts * segfault due to not checking drop flag properly * debuginfo for DST smart pointers * unreachable code in drop glue
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⌛ Testing commit 4446d44 with merge 17a4e3c... |
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💔 Test failed - auto-mac-64-opt |
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⌛ Testing commit b799cd8 with merge 32f3bff... |
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⛄ The build was interrupted to prioritize another pull request. |
bors
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May 13, 2015
r? @nikomatsakis (note a few TODOs left in the code where I wasn't sure about stuff).
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This was referenced May 15, 2015
bors
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May 16, 2015
Most of `Rc`’s trait implementations were DST-ified in #24619, but not these ones.
This was referenced Mar 6, 2017
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 10, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 10, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 11, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
pushed a commit
to arielb1/rust
that referenced
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Mar 11, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
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r? @nikomatsakis (note a few TODOs left in the code where I wasn't sure about stuff).