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Fixed unsoundness of using `&mut MaybeUninit<T>` as the out type for … #1

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danielhenrymantilla merged 5 commits into master from introduce_out_refs

Feb 29, 2020

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danielhenrymantilla commented Jan 30, 2020 •

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This (WIP) PR objective is to fix the issues spotted by @Kixunil (thanks for telling me!):

Minor: using transmute on fat references makes incorrect assumptions about their layout, so that code could break in a future version of Rust.
- Fixed by using slice::from_raw_parts{,_mut} instead.
MAJOR: The API used &mut MaybeUninit<_> as its &out reference type, assuming that it was sound to transmute between &mut T and &mut MaybeUninit<T>, which it is not (see Document that casting &mut T to &mut MaybeUninit<T> is not safe rust-lang/rust#66699)
- Fixed by using a custom abstraction over &out references that does not let writing MaybeUninit::uninit() into the pointee.
Added some API features, such as being able to forge a &out T from &mut ManuallyDrop<T> (to offer &out refs even when T : !Copy and could thus have drop glue (although leaking is safe, I take an opinionated stance here that so doing ought to be visible and thus verbose)

@HeroicKatora do you wanna review this?

TODO:

Document new methods
Add extra helpers to Out references


          Fixed unsoundness of using &mut MaybeUninit<T> as the out type for …

62a5a14

…`&mut T`

danielhenrymantilla added the wip label

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          Various improvements as suggested by @HeroicKatora

e3926f9

It features:

  - enhancing `Vec::reserve_uninit` to a more general API for accessing with the backing buffer / capacity of a Vec;

  - Rename `idx` to `.get_out`

  - (Ab)use `.copy_from_slice()` in read implementations to use less unsafe

TODO:

  - The iterator API,

  - Documentation

Co-Authored-By: Andreas Molzer <andreas.molzer@gmx.de>

danielhenrymantilla force-pushed the introduce_out_refs branch from e9f9568 to e3926f9 Compare

February 7, 2020 20:24

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Some TODOs

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Typos

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          Improve docs, start implementing iteration logic

ce8f8bc

danielhenrymantilla force-pushed the introduce_out_refs branch from 42dc756 to ce8f8bc Compare

February 10, 2020 23:49


          Unified Out and OutSlice into a single Out<T : ?Sized> typeå

634fec7

Not only does this lead to replacing `OutSlice<T>` with the more readable
`Out<[T]>`, it also results in other parts of the API being greatly simplified
(mainly the `AsOut` trait).

HeroicKatora reviewed

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HeroicKatora left a comment

Review, round two. The interface with Out works great! The core of it came together very well. There are a few nits, documentation and naming, but no direct unsoundess that I could find.

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          Improve code as per @HeroicKatora suggestions.

91d4ee7

Co-Authored-By: Andreas Molzer <andreas.molzer@gmx.de>

danielhenrymantilla added enhancement and removed wip labels

danielhenrymantilla merged commit f884ca3 into master

danielhenrymantilla deleted the introduce_out_refs branch

March 1, 2020 00:45

danielhenrymantilla restored the introduce_out_refs branch

September 29, 2020 21:01

danielhenrymantilla deleted the introduce_out_refs branch

September 30, 2020 09:32

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