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These debug assertions are all implemented only at runtime using
`const_eval_select`, and in the error path they execute
`intrinsics::abort` instead of being a normal debug assertion to
minimize the impact of these assertions on code size, when enabled.
Of all these changes, the bounds checks for unchecked indexing are
expected to be most impactful (case in point, they found a problem in
rustc).
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Refactor set_ptr_value as with_metadata_of
Replaces `set_ptr_value` (#75091) with methods of reversed argument order:
```rust
impl<T: ?Sized> *mut T {
pub fn with_metadata_of<U: ?Sized>(self, val: *mut U) -> *mut U;
}
impl<T: ?Sized> *const T {
pub fn with_metadata_of<U: ?Sized>(self, val: *const U) -> *const U;
}
```
By reversing the arguments we achieve several clarifications:
- The function closely resembles `cast` with an argument to
initialize the metadata. This is easier to teach and answers a long
outstanding question that had restricted cast to `Sized` pointee
targets. See multiples reviews of
<https://github.com/rust-lang/rust/pull/47631>
- The 'object identity', in the form of provenance, is now preserved
from the receiver argument to the result. This helps explain the method as
a builder-style, instead of some kind of setter that would modify
something in-place. Ensuring that the result has the identity of the
`self` argument is also beneficial for an intuition of effects.
- An outstanding concern, 'Correct argument type', is avoided by not
committing to any specific argument type. This is consistent with cast
which does not require its receiver to be a 'raw address'.
Hopefully the usage examples in `sync/rc.rs` serve as sufficient examples of the style to convince the reader of the readability improvements of this style, when compared to the previous order of arguments.
I want to take the opportunity to motivate inclusion of this method _separate_ from metadata API, separate from `feature(ptr_metadata)`. It does _not_ involve the `Pointee` trait in any form. This may be regarded as a very, very light form that does not commit to any details of the pointee trait, or its associated metadata. There are several use cases for which this is already sufficient and no further inspection of metadata is necessary.
- Storing the coercion of `*mut T` into `*mut dyn Trait` as a way to dynamically cast some an arbitrary instance of the same type to a dyn trait instance. In particular, one can have a field of type `Option<*mut dyn io::Seek>` to memorize if a particular writer is seekable. Then a method `fn(self: &T) -> Option<&dyn Seek>` can be provided, which does _not_ involve the static trait bound `T: Seek`. This makes it possible to create an API that is capable of utilizing seekable streams and non-seekable streams (instead of a possible less efficient manner such as more buffering) through the same entry-point.
- Enabling more generic forms of unsizing for no-`std` smart pointers. Using the stable APIs only few concrete cases are available. One can unsize arrays to `[T]` by `ptr::slice_from_raw_parts` but unsizing a custom smart pointer to, e.g., `dyn Iterator`, `dyn Future`, `dyn Debug`, can't easily be done generically. Exposing `with_metadata_of` would allow smart pointers to offer their own `unsafe` escape hatch with similar parameters where the caller provides the unsized metadata. This is particularly interesting for embedded where `dyn`-trait usage can drastically reduce code size.
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impl From<&[T; N]> and From<&mut [T; N]> for Vec<T>
I really wanted to write:
```rust
fn example(a: impl Into<Vec<u8>>) {}
fn main() {
example(b"raw");
}
```
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Docs: make Vec::from_raw_parts documentation less strict
This is my first PR; be gentle!
In https://users.rust-lang.org/t/why-does-vec-from-raw-parts-require-same-size-and-not-same-size-capacity/73036/2?u=janpaul123 it was suggested to me that I should make a PR to make the documentation of `Vec::from_raw_parts` less strict, since we don't require `T` to have the same size, just `size_of::<T>() * capacity` to be the same, since that is what results in `Layout::size` being the same in `dealloc`, which is really what matters.
Also in https://users.rust-lang.org/t/why-does-vec-from-raw-parts-require-same-size-and-not-same-size-capacity/73036/8?u=janpaul123 it was suggested that it's better to use `slice::from_raw_parts`, which I think is useful advise that could also be mentioned in the docs, so I added that too.
Let me know what you think! :)
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ChayimFriedman2:allow-comparing-vecs-with-different-allocators, r=dtolnay
Allow comparing `Vec`s with different allocators using `==`
See https://stackoverflow.com/q/71021633/7884305.
I did not changed the `PartialOrd` impl too because it was not generic already (didn't support `Vec<T> <=> Vec<U> where T: PartialOrd<U>`).
Does it needs tests?
I don't think this will hurt type inference much because the default allocator is usually not inferred (`new()` specifies it directly, and even with other allocators, you pass the allocator to `new_in()` so the compiler usually knows the type).
I think this requires FCP since the impls are already stable.
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lopopolo:lopopolo/string-try-reserve-exact-doc-typo, r=Dylan-DPC
Fix typo in `String::try_reserve_exact` docs
Copying the pattern from `Vec::try_reserve_exact` and `String::try_reserve`,
it looks like this doc comment is intending to refer to the currently-being-documented
function.
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Copying the pattern from `Vec::try_reserve_exact` and `String::try_reserve`,
it looks like this doc comment is intending to refer to the currently-being-documented
function.
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Hermit now properly separates kernel from userspace.
Applications for hermit can now use Rust's default alloc_error_handler instead of calling the kernel's __rg_oom.
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Co-authored-by: Daniel Henry-Mantilla <daniel.henry.mantilla@gmail.com>
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add module-level documentation for vec's in-place iteration
As requested in the last libs team meeting and during previous reviews.
Feel free to point out any gaps you encounter, after all non-obvious things may with hindsight seem obvious to me.
r? `@yaahc`
CC `@steffahn`
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By reversing the arguments we achieve several clarifications:
- The function closely resembles `cast` but with an argument to
initialized the metadata. This is easier to teach and answers an long
outstanding question that had restricted cast to `Sized` targets
initially. See multiples reviews of
<https://github.com/rust-lang/rust/pull/47631>
- The 'object identity', in the form or provenance, is now preserved
from the call receiver to the result. This helps explain the method as
a builder-style, instead of some kind of setter that would modify
something in-place. Ensuring that the result has the identity of the
`self` argument is also beneficial for an intuition of effects.
- An outstanding concern, 'Correct argument type', is avoided by not
committing to any specific argument type. This is consistent with cast
which does not require its receiver to be a raw address.
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Inspired by this internals thread: https://internals.rust-lang.org/t/rc-optimization-on-64-bit-targets/16362
[The generated assembly is a bit smaller](https://rust.godbolt.org/z/TeTnf6144) and is a more efficient usage of the CPU's instruction cache. `unlikely` doesn't impact any of the small artificial tests I've done, but I've included it in case it might help more complex scenarios when this is inlined.
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Neither the number of elements in a vector can overflow a `usize`, nor
can the amount of elements in two vectors.
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BTreeMap::entry: Avoid allocating if no insertion
This PR allows the `VacantEntry` to borrow from an empty tree with no root, and to lazily allocate a new root node when the user calls `.insert(value)`.
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This is my first PR; be gentle!
In https://users.rust-lang.org/t/why-does-vec-from-raw-parts-require-same-size-and-not-same-size-capacity/73036/2?u=janpaul123 it was suggested to me that I should make a PR to make the documentation of `Vec::from_raw_parts` less strict, since we don't require `T` to have the same size, just `size_of::<T>() * capacity` to be the same, since that is what results in `Layout::size` being the same in `dealloc`, which is really what matters.
Also in https://users.rust-lang.org/t/why-does-vec-from-raw-parts-require-same-size-and-not-same-size-capacity/73036/8?u=janpaul123 it was suggested that it's better to use `slice::from_raw_parts`, which I think is useful advise that could also be mentioned in the docs, so I added that too.
Let me know what you think! :)
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Made the fields of VecDeque's Iter private by creating a Iter::new(...) function to create a new instance of Iter and migrating usage to use Iter::new(...).
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Use MaybeUninit in VecDeque to remove the undefined behavior of slice
Signed-off-by: JmPotato <ghzpotato@gmail.com>
Ref https://github.com/rust-lang/rust/issues/74189. Adjust the code to follow the [doc.rust-lang.org/reference/behavior-considered-undefined.html](https://doc.rust-lang.org/reference/behavior-considered-undefined.html).
* Change the return type of `buffer_as_slice` from `&[T]` to `&[MaybeUninit<T>]`.
* Add some corresponding safety comments.
Benchmark results:
master 8d6f527530f4ba974d922269267fe89050188789
```rust
test collections::vec_deque::tests::bench_pop_back_100 ... bench: 47 ns/iter (+/- 1)
test collections::vec_deque::tests::bench_pop_front_100 ... bench: 50 ns/iter (+/- 4)
test collections::vec_deque::tests::bench_push_back_100 ... bench: 69 ns/iter (+/- 10)
test collections::vec_deque::tests::bench_push_front_100 ... bench: 72 ns/iter (+/- 6)
test collections::vec_deque::tests::bench_retain_half_10000 ... bench: 145,891 ns/iter (+/- 7,975)
test collections::vec_deque::tests::bench_retain_odd_10000 ... bench: 141,647 ns/iter (+/- 3,711)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench: 120,132 ns/iter (+/- 4,078)
```
This PR
```rust
test collections::vec_deque::tests::bench_pop_back_100 ... bench: 48 ns/iter (+/- 2)
test collections::vec_deque::tests::bench_pop_front_100 ... bench: 51 ns/iter (+/- 3)
test collections::vec_deque::tests::bench_push_back_100 ... bench: 73 ns/iter (+/- 2)
test collections::vec_deque::tests::bench_push_front_100 ... bench: 73 ns/iter (+/- 2)
test collections::vec_deque::tests::bench_retain_half_10000 ... bench: 131,796 ns/iter (+/- 5,440)
test collections::vec_deque::tests::bench_retain_odd_10000 ... bench: 137,563 ns/iter (+/- 3,349)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench: 128,815 ns/iter (+/- 3,289)
```
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Improve doc wording for retain on some collections
I found the documentation wording on the various retain methods on many collections to be unusual.
I tried to invert the relation by switching `such that` with `for which` .
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r=Mark-Simulacrum
Use modern formatting for format! macros
This updates the standard library's documentation to use the new format_args syntax.
The documentation is worthwhile to update as it should be more idiomatic
(particularly for features like this, which are nice for users to get acquainted
with). The general codebase is likely more hassle than benefit to update: it'll
hurt git blame, and generally updates can be done by folks updating the code if
(and when) that makes things more readable with the new format.
A few places in the compiler and library code are updated (mostly just due to
already having been done when this commit was first authored).
`eprintln!("{}", e)` becomes `eprintln!("{e}")`, but `eprintln!("{}", e.kind())` remains untouched.
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This updates the standard library's documentation to use the new syntax. The
documentation is worthwhile to update as it should be more idiomatic
(particularly for features like this, which are nice for users to get acquainted
with). The general codebase is likely more hassle than benefit to update: it'll
hurt git blame, and generally updates can be done by folks updating the code if
(and when) that makes things more readable with the new format.
A few places in the compiler and library code are updated (mostly just due to
already having been done when this commit was first authored).
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Signed-off-by: JmPotato <ghzpotato@gmail.com>
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BTree: remove dead data needlessly complicating insert
Possibly needless instructions generated
r? rust-lang/libs
r? ``@Amanieu``
cc ``@frank-king``
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fix typo in btree/vec doc: Self -> self
this pr fixes #92345
the documentation refers to the object the method is called for, not the type, so it should be using the lower case self.
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