The existence of these two functions is at odds with our current [error
conventions][conventions] which recommend that panicking and `Result`-like
variants should not be provided together.
[conventions]: https://github.com/rust-lang/rfcs/blob/master/text/0236-error-conventions.md#do-not-provide-both-result-and-fail-variants
This commit adds a new `borrow_state` function returning a `BorrowState` enum to
`RefCell` which serves as a replacemnt for the `try_borrow` and `try_borrow_mut`
functions.
Functions are needed for safety and convenience.
It is a common pattern to use `mem::transmute` to convert between
`Box` and raw pointer, like this:
```
let b = Box::new(3);
let p = mem::transmute(b);
// pass `p` to some C library
```
After this commit, conversion can be written as:
```
let p = b.into_raw();
```
`into_raw` and `from_raw` functions are still unsafe, but they are
much safer than `mem::transmute`, because *raw functions do not
convert between incompatible pointers. For example, this likely
incorrect code can be successfully compiled:
```
let p: *mut u64 = ...
let b: Box<u32> = mem::transmute(p);
```
Using `from_raw` results in compile-time error:
```
let p: *mut u64 = ...
let b: Box<u32> = Box::from_raw(p); // compile-time error
```
`into_raw` and `from_raw` functions are similar to C++ `std::unique_ptr`
`release` function [1] and constructor from pointer [2].
[1] http://en.cppreference.com/w/cpp/memory/unique_ptr/release
[2] http://en.cppreference.com/w/cpp/memory/unique_ptr/unique_ptr
The new `::ops::Range` has separated implementations for each of the
numeric types, while the old `::iter::Range` has one for type `Int`.
However, we do not take output bindings into account when selecting
traits. So it confuses `typeck` and makes the new range does not work as
good as the old one when it comes to type inference.
This patch implements `Iterator` for the new range for one type `Int`.
This limitation could be lifted, however, if we ever reconsider the
output types' role in type inference.
Closes#21595Closes#21649Closes#21672
Functions are needed for safety and convenience.
It is a common pattern to use `mem::transmute` to convert between
`Box` and raw pointer, like this:
```
let b = Box::new(3);
let p = mem::transmute(b);
// pass `p` to some C library
```
After this commit, conversion can be written as:
```
let p = boxed::into_raw(b);
```
`into_raw` and `from_raw` functions are still unsafe, but they are
much safer than `mem::transmute`, because *raw functions do not
convert between incompatible pointers. For example, this likely
incorrect code can be successfully compiled:
```
let p: *mut u64 = ...
let b: Box<u32> = mem::transmute(p);
```
Using `from_raw` results in compile-time error:
```
let p: *mut u64 = ...
let b: Box<u32> = Box::from_raw(p); // compile-time error
```
`into_raw` and `from_raw` functions are similar to C++ `std::unique_ptr`
`release` function [1] and constructor from pointer [2].
[1] http://en.cppreference.com/w/cpp/memory/unique_ptr/release
[2] http://en.cppreference.com/w/cpp/memory/unique_ptr/unique_ptr
Currently, we only infer the kind of a closure based on the expected type or explicit annotation. If neither applies, we currently report an error. This pull request changes that case to defer the decision until we are able to analyze the actions of the closure: closures which mutate their environment require `FnMut`, closures which move out of their environment require `FnOnce`.
This PR is not the end of the story:
- It does not remove the explicit annotations nor disregard them. The latter is the logical next step to removing them (we'll need a snapshot before we can do anything anyhow). Disregarding explicit annotations might expose more bugs since right now all closures in libstd/rustc use explicit annotations or the expected type, so this inference never kicks in.
- The interaction with instantiating type parameter fallbacks leaves something to be desired. This is mostly just saying that the algorithm from https://github.com/rust-lang/rfcs/pull/213 needs to be implemented, which is a separate bug. There are some semi-subtle interactions though because not knowing whether a closure is `Fn` vs `FnMut` prevents us from resolving obligations like `F : FnMut(...)`, which can in turn prevent unification of some type parameters, which might (in turn) lead to undesired fallback. We can improve this situation however -- even if we don't know whether (or just how) `F : FnMut(..)` holds or not for some closure type `F`, we can still perform unification since we *do* know the argument and return types. Once kind inference is done, we can complete the `F : FnMut(..)` analysis -- which might yield an error if (e.g.) the `F` moves out of its environment.
r? @nick29581
specialized to closures, and invoke them as soon as we know the
closure kind. I thought initially we would need a fixed-point
inference algorithm but it appears I was mistaken, so we can do this.
upvar inference. Upvar inference can cause some obligations to be
deferred, notably things like `F : Sized` where `F` is a closure type,
or `F : FnMut`. Adjust the ordering therefore so that we process all
traits and apply fallback, do upvar inference, and only then start
reporting errors for outstanding obligations.
doing the final checking for closure calls until after trait inference
is performed. This isn't important now, but it's essential if we are to
delay inferring the closure kind.
Removes `Copy` from `ops::Range` (`a..b`) and `ops::RangeFrom` (`a..`)
[breaking-change]
---
I forgot about these two in #20790, this PR also adds `Clone` to the `Peekable` adapter which used to be `Copy`able.
r? @nikomatsakis or anyone
The new `::ops::Range` has separated implementations for each of the
numeric types, while the old `::iter::Range` has one for type `Int`.
However, we do not take output bindings into account when selecting
traits. So it confuses `typeck` and makes the new range does not work as
good as the old one when it comes to type inference.
This patch implements `Iterator` for the new range for one type `Int`.
This limitation could be lifted, however, if we ever reconsider the
output types' role in type inference.
Closes#21595Closes#21649Closes#21672
Update the coherence rules to "covered first" -- the first type parameter to contain either a local type or a type parameter must contain only covered type parameters.
cc #19470.
Fixes#20974.
Fixes#20749.
r? @aturon
An alternative to #21749.
This also refactors the naming lint code a little bit and slightly rephrases some warnings (`uppercase` → `upper case`).
Closes#21735.
