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## Summary Closures should capture their upvars by value unless the `ref` keyword is used. ## Motivation For unboxed closures, we will need to syntactically distinguish between captures by value and captures by reference. ## Detailed design...
## Summary Change the semantics of the built-in fixed-size integer types from being defined as wrapping around on overflow to it being considered a program error (but *not* undefined behavior in the C sense). Implementations are *permitted*...
## Summary Remove the coercion from `Box<T>` to `&T` from the language. ## Motivation The coercion between `Box<T>` to `&T` is not replicable by user-defined smart pointers and has been found to be rarely used [1]. We already removed the co...
## Summary * Remove the `crate_id` attribute and knowledge of versions from rustc. * Add a `#[crate_name]` attribute similar to the old `#[crate_id]` attribute * Filenames will no longer have versions, nor will symbols * A new flag, `--exte...
## Summary Require a feature gate to expose private items in public APIs, until we grow the appropriate language features to be able to remove the feature gate and forbid it entirely. ## Motivation Privacy is central to guaranteeing the inv...
## Summary This RFC proposes to 1. Expand the rules for eliding lifetimes in `fn` definitions, and 2. Follow the same rules in `impl` headers. By doing so, we can avoid writing lifetime annotations ~87% of the time that they are currently r...
## Summary *Note:* This RFC discusses the behavior of `rustc`, and not any changes to the language. Change how target specification is done to be more flexible for unexpected usecases. Additionally, add support for the "unknown" OS in targe...
## Summary Rename the `Share` trait to `Sync` ## Motivation With interior mutability, the name "immutable pointer" for a value of type `&T` is not quite accurate. Instead, the term "shared reference" is becoming popular to reference values...
## Summary Remove or feature gate the shadowing of view items on the same scope level, in order to have less complicated semantic and be more future proof for module system changes or experiments. This means the names brought in scope by `e...
## Summary Rename `*T` to `*const T`, retain all other semantics of unsafe pointers. ## Motivation Currently the `T*` type in C is equivalent to `*mut T` in Rust, and the `const T*` type in C is equivalent to the `*T` type in Rust. Noticeab...
## Summary Currently we use inference to find the current type of otherwise-unannotated integer literals, and when that fails the type defaults to `int`. This is often felt to be potentially error-prone behavior. This proposal removes the i...
## Summary Cleanup the trait, method, and operator semantics so that they are well-defined and cover more use cases. A high-level summary of the changes is as follows: 1. Generalize explicit self types beyond `&self` and `&mut self` etc, so...
## Summary Do not identify struct literals by searching for `:`. Instead define a sub- category of expressions which excludes struct literals and re-define `for`, `if`, and other expressions which take an expression followed by a block (or...
## Summary Remove localization features from format!, and change the set of escapes accepted by format strings. The `plural` and `select` methods would be removed, `#` would no longer need to be escaped, and `{{`/`}}` would become escapes f...
## Summary `Index` should be split into `Index` and `IndexMut`. ## Motivation Currently, the `Index` trait is not suitable for most array indexing tasks. The slice functionality cannot be replicated using it, and as a result the new `Vec` h...
## Summary Remove the coercion from `Box<T>` to `&mut T` from the language. ## Motivation Currently, the coercion between `Box<T>` to `&mut T` can be a hazard because it can lead to surprising mutation where it was not expected. ## Detailed...
## Summary Add syntax sugar for importing a module and items in that module in a single view item. ## Motivation Make use clauses more concise. ## Detailed design The `mod` keyword may be used in a braced list of modules in a `use` item to...
## Summary Rust currently forbids pattern guards on match arms with move-bound variables. Allowing them would increase the applicability of pattern guards. ## Motivation Currently, if you attempt to use guards on a match arm with a move-bou...
## Summary Add a `partial_cmp` method to `PartialOrd`, analogous to `cmp` in `Ord`. ## Motivation The `Ord::cmp` method is useful when working with ordered values. When the exact ordering relationship between two values is required, `cmp` i...
## Summary Allow users to load custom lints into `rustc`, similar to loadable syntax extensions. ## Motivation There are many possibilities for user-defined static checking: * Enforcing correct usage of Servo's [JS-managed pointers](https:/...
"Vecs in Rust in general, are crazy fast; faster than I can replicate in C. Amazing."