Update `fn()` trait implementation docs
Fixes#119903
This was FCP'd and approved for the 1.70.0 release, this is just a docs update to match that change.
Docs: Use non-SeqCst in module example of atomics
I done this for this reasons:
1. The example now shows that there is more Orderings than just SeqCst.
2. People who would copy from example would now have more suitable orderings for the job.
3. SeqCst is both much harder to reason about and not needed in most situations.
IMHO, we should encourage people to think and use memory orderings that is suitable to task instead of blindly defaulting to SeqCst.
r? `@m-ou-se`
Consolidate all associated items on the NonZero integer types into a single impl block per type
**Before:**
```rust
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(1)]
pub struct NonZeroI8(i8);
impl NonZeroI8 {
pub const fn new(n: i8) -> Option<Self> ...
pub const fn get(self) -> i8 ...
}
impl NonZeroI8 {
pub const fn leading_zeros(self) -> u32 ...
pub const fn trailing_zeros(self) -> u32 ...
}
impl NonZeroI8 {
pub const fn abs(self) -> NonZeroI8 ...
}
...
```
**After:**
```rust
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(1)]
pub struct NonZeroI8(i8);
impl NonZeroI8 {
pub const fn new(n: i8) -> Option<Self> ...
pub const fn get(self) -> i8 ...
pub const fn leading_zeros(self) -> u32 ...
pub const fn trailing_zeros(self) -> u32 ...
pub const fn abs(self) -> NonZeroI8 ...
...
}
```
Having 6-7 different impl blocks per type is not such a problem in today's implementation, but becomes awful upon the switch to a generic `NonZero<T>` type (context: https://github.com/rust-lang/rust/issues/82363#issuecomment-921513910).
In the implementation from https://github.com/rust-lang/rust/pull/100428, there end up being **67** impl blocks on that type.
<img src="https://github.com/rust-lang/rust/assets/1940490/5b68bd6f-8a36-4922-baa3-348e30dbfcc1" width="200"><img src="https://github.com/rust-lang/rust/assets/1940490/2cfec71e-c2cd-4361-a542-487f13f435d9" width="200"><img src="https://github.com/rust-lang/rust/assets/1940490/2fe00337-7307-405d-9036-6fe1e58b2627" width="200">
Without the refactor to a single impl block first, introducing `NonZero<T>` would be a usability regression compared to today's separate pages per type. With all those blocks expanded, Ctrl+F is obnoxious because you need to skip 12× past every match you don't care about. With all the blocks collapsed, Ctrl+F is useless. Getting to a state in which exactly one type's (e.g. `NonZero<u32>`) impl blocks are expanded while the rest are collapsed is annoying.
After this refactor to a single impl block, we can move forward with making `NonZero<T>` a generic struct whose docs all go on the same rustdoc page. The rustdoc will have 12 impl blocks, one per choice of `T` supported by the standard library. The reader can expand a single one of those impl blocks e.g. `NonZero<u32>` to understand the entire API of that type.
Note that moving the API into a generic `impl<T> NonZero<T> { ... }` is not going to be an option until after `NonZero<T>` has been stabilized, which may be months or years after its introduction. During the period while generic `NonZero` is unstable, it will be extra important to offer good documentation on all methods demonstrating the API being used through the stable aliases such as `NonZeroI8`.
This PR follows a `key = $value` syntax for the macros which is similar to the macros we already use for producing a single large impl block on the integer primitives.
1dd4db5062/library/core/src/num/mod.rs (L288-L309)
Best reviewed one commit at a time.
Add private `NonZero<T>` type alias.
According to step 2 suggested in https://github.com/rust-lang/rust/pull/100428#pullrequestreview-1767139731.
This adds a private type alias for `NonZero<T>` so that some parts of the code can already start using `NonZero<T>` syntax.
Using `NonZero<T>` for `convert` and other parts which implement `From` doesn't work while it is a type alias, since this results in conflicting implementations.
Tune the inlinability of `unwrap`
Fixes#115463
cc `@thomcc`
This tweaks `unwrap` on ~~`Option` &~~ `Result` to be two parts:
- `#[inline(always)]` for checking the discriminant
- `#[cold]` for actually panicking
The idea here is that checking the discriminant on a `Result` ~~or `Option`~~ should always be trivial enough to be worth inlining, even in `opt-level=z`, especially compared to passing it to a function.
As seen in the issue and codegen test, this will hopefully help particularly for things like `.try_into().unwrap()`s that are actually infallible, but in a way that's only visible with the inlining.
EDIT: I've restricted this to `Result` to avoid combining effects
Later in this stack, as the nonzero_integers macro is going to be
responsible for producing a larger fraction of the API for the NonZero
integer types, it will need to receive a number of additional arguments
beyond the ones currently seen here.
Additional arguments, especially named arguments across multiple lines,
will turn out clearer if everything in one macro call is for the same
NonZero type.
This commit adopts a similar arrangement to what we do for generating
the API of the integer primitives (`impl u8` etc), which also generate a
single type's API per top-level macro call, rather than generating all
12 impl blocks for the 12 types from one macro call.
This way all the other macros defined in this module, such as
nonzero_leading_trailing_zeros, are available to call within the expansion of
nonzero_integers.
(Macros defined by macro_rules cannot be called from the same module above the
location of the macro_rules.)
In this commit the ability to call things like nonzero_leading_trailing_zeros is
not immediately used, but later commits in this stack will be consolidating the
entire API of NonZeroT to be generated through nonzero_integers, and will need
to make use of some of the other macros to do that.
A more efficient slice comparison implementation for T: !BytewiseEq
(This is a follow up PR on #113654)
This PR changes the implementation for `[T]` slice comparison when `T: !BytewiseEq`. The previous implementation using zip was not optimized properly by the compiler, which didn't leverage the fact that both length were equal. Performance improvements are for example 20% when testing that `[Some(0_u64); 4096].as_slice() == [Some(0_u64); 4096].as_slice()`.
Use `assert_unsafe_precondition` for `char::from_u32_unchecked`
Use `assert_unsafe_precondition` in `char::from_u32_unchecked` so that it can be stabilized as `const`.
Rewrite `pin` module documentation to clarify usage and invariants
The documentation of `pin` today does not give a complete treatment of pinning from first principles, nor does it adequately help build intuition and understanding for how the different elements of the pinning story fit together.
This rewrite attempts to address these in a way that makes the concept more approachable while also making the documentation more normative.
This PR picks up where `@mcy` left off in #88500 (thanks to him for the original work and `@Manishearth` for mentioning it such that I originally found it). I've directly incorporated much of the feedback left on the original PR and have rewritten and changed some of the main conceits of the prose to better adhere to the feedback from the reviewers on that PR or just explain something in (hopefully) a better way.
