initial commit

Author: Pointerbender

.gitignore

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+/target
+Cargo.lock

CONTRIBUTING.md

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+At this point, this project does not accept pull requests yet. Please check back later!

Cargo.toml

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+#cargo-features = ["rust-version"]
+
+[package]
+name = "deferred-reference"
+version = "0.1.0"
+authors = ["Pointerbender"]
+#rust-version = "1.51.0"
+edition = "2018"
+license = "MIT"
+
+[features]
+# default = []
+default = ["unstable"]
+unstable = ["slice_ptr_len", "coerce_unsized"]
+slice_ptr_len = []
+coerce_unsized = []
+
+[dependencies]

LICENSE.md

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+Copyright 2021 Pointerbender
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# Deferred Reference
+This crate helps with creating multiple mutable references to the contents of a variable without triggering undefined behavior.
+The Rust borrow rules dictate that it is undefined behavior to create more than one mutable reference to the same region,
+even if the mutable reference is not used. However, this can sometimes be a tad too restrictive if the programmer knows
+that two mutable references will not overlap. Using raw pointers, it is already possible to work-around the Rust borrow rules today,
+but this requires wizard-like skills and in-depth knowledge of handling raw pointers and this is more prone to error than
+using Rust references. With the introduction of non-lexical lifetimes in the Rust 2018 edition, the ergonomics around references 
+have already significantly improved, but there are still some corner-cases where the programmer wished there was some way
+to create non-overlapping mutable references into the same location (e.g. disjoint indices of a slice or array), without
+resorting to manually managed raw pointers. In order to aid with this, this crate introduces the concept of a
+"*deferred reference*"<sup >[1](#footnote1)</a></sup>. A deferred reference is almost exactly like a regular reference
+(e.g. a `&T` or a `&mut T`), but it differs from a regular reference in the following ways:
+* A deferred reference is not an actual reference, it is merely a smart pointer tied to the lifetime of the location it points to
+  (regular raw pointers always have a static lifetime, and can thus become dangling if the location it points to is moved or dropped).
+* It is allowed to keep multiple deferred mutable references around (as long as these are not dereferenced in a way so that
+  these create an overlap between a mutable reference and another (de)reference).
+
+## Getting started
+If you're on nightly Rust, add the following dependency to your `Cargo.toml`:
+
+```toml
+[dependencies]
+deferred_reference = { version = "0.1.0" }
+```
+
+This crate uses some unstable features, but it also works on stable Rust with less features.
+For using this crate in stable Rust you need to disable the unstable nightly features using the `default-features` flag, like so:
+
+```toml
+[dependencies]
+deferred_reference = { version = "0.1.0", default-features = false }
+```
+
+Please see the documentation for this crate on how to get started with some concrete code examples.
+
+## `#![no_std]` environments
+This crate is entirely `#![no_std]` and does not depend on the `alloc` crate. No additional `Cargo.toml` features need to be configured
+in order to support `#![no_std]` environments. This crate also does not have any dependencies in its `Cargo.toml`.
+
+## Miri tested
+This crate is extensively tested using [Miri](https://github.com/rust-lang/miri) using the `-Zmiri-track-raw-pointers` flag:
+```bash
+$ MIRIFLAGS="-Zmiri-track-raw-pointers" cargo miri test
+```
+Miri follows the [Stacked Borrows](https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md) model
+(by Ralf Jung et al.) and so does this crate. If you happen to spot any violations of this model in this crate, feel free
+to open a Github issue!
+
+## License
+This project is licensed under the MIT license. Please see the file `LICENSE.md` in the root of this project for the full license text.
+
+## Contributing
+It is encouraged to open a Github issue if you run into problems or if you have a feature request.
+At this point, this project does not accept pull requests yet. Please check back later!
+
+## Footnotes
+<a name="footnote1"></a>
+[1]: The concept of "deferred references" is inspired by the concept of "[Deferred Borrows](https://c1f.net/pubs/ecoop2020_defborrow.pdf)"
+     authored by Chris Fallin. However, these are not entirely the same concept. These differ in the sense that deferred borrows bring
+     an extension to the Rust type system (called *static path-dependent types*) and its implementation is intended to live within the
+     Rust compiler, while deferred references are implemented in Rust code that is already possible today with its existing type system.
+     The trade-off made here is that this requires minimal use of `unsafe` code blocks with deferred references, while deferred borrows
+     would work entirely within "safe Rust" if these were to be implemented in the Rust compiler. There are also some similarities between
+     the two concepts: both concepts are statically applied during compile-time and due not incur any runtime overhead. Also, with both
+     approaches an actual reference is not created until the reference is actually in use (i.e. dereferenced or borrowed for an extended
+     period of time).