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Update vec.rs
Add a warning not to convert char* from c to Vec<u8> (I thought you could until I asked on irc).
Reasoning is that it will help people avoid an error that could cause crashes and undefined behaviour. Only drawback is that it could confuse someone not familiar with C, but beginners are unlikely to be using this function anyway.
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Replace uses of `#[unsafe_destructor_blind_to_params]` with `#[may_dangle]`
CC #34761
r? @pnkfelix
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Changed language to stress char is the C meaning (u8) not unicode.
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Add a warning not to convert char* from c to Vec<u8> (I thought you could until I asked on irc)
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CC #34761
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Specialize to use copy_from_slice when extending a Vec with &[T] where
T: Copy.
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These iterators can use a pointer comparison instead of computing the length.
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Vec::from_iter's general case allocates the vector up front;
this is redundant for the TrustedLen case, and can then be avoided
to reduce the size of the code.
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Since I said "no intentional functional change" in the previous commit,
I guess it was inevitable there were unintentional changes. Not
functional, but optimization-wise. This restores the extend
specialization's use in Vec::from_iter.
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As far as possible, use regular `default fn` specialization in favour of
ad-hoc conditionals.
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Add Iterator trait TrustedLen to enable better FromIterator / Extend
This trait attempts to improve FromIterator / Extend code by enabling it to trust the iterator to produce an exact number of elements, which means that reallocation needs to happen only once and is moved out of the loop.
`TrustedLen` differs from `ExactSizeIterator` in that it attempts to include _more_ iterators by allowing for the case that the iterator's len does not fit in `usize`. Consumers must check for this case (for example they could panic, since they can't allocate a collection of that size).
For example, chain can be TrustedLen and all numerical ranges can be TrustedLen. All they need to do is to report an exact size if it fits in `usize`, and `None` as the upper bound otherwise.
The trait describes its contract like this:
```
An iterator that reports an accurate length using size_hint.
The iterator reports a size hint where it is either exact
(lower bound is equal to upper bound), or the upper bound is `None`.
The upper bound must only be `None` if the actual iterator length is
larger than `usize::MAX`.
The iterator must produce exactly the number of elements it reported.
This trait must only be implemented when the contract is upheld.
Consumers of this trait must inspect `.size_hint()`’s upper bound.
```
Fixes #37232
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Most of the Rust community agrees that the vec! macro is clearer when
called using square brackets [] instead of regular brackets (). Most of
these ocurrences are from before macros allowed using different types of
brackets.
There is one left unchanged in a pretty-print test, as the pretty
printer still wants it to have regular brackets.
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This now produces as good code (with optimizations) using the TrustedLen
codepath.
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Implement `From<Cow<str>> for String` and `From<Cow<[T]>> for Vec<T>`.
Motivation: the `selectors` crate is generic over a string type, in order to support all of `String`, `string_cache::Atom`, and `gecko_string_cache::Atom`. Multiple trait bounds are used for the various operations done with these strings. One of these operations is creating a string (as efficiently as possible, re-using an existing memory allocation if possible) from `Cow<str>`.
The `std::convert::From` trait seems natural for this, but the relevant implementation was missing before this PR. To work around this I’ve added a `FromCowStr` trait in `selectors`, but with trait coherence that means one of `selectors` or `string_cache` needs to depend on the other to implement this trait. Using a trait from `std` would solve this.
The `Vec<T>` implementation is just added for consistency. I also tried a more general `impl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O`, but (the compiler thinks?) it conflicts with `From<T> for T` the impl (after moving all of `collections::borrow` into `core::borrow` to work around trait coherence).
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Add missing urls on Vec docs
r? @steveklabnik
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Motivation: the `selectors` crate is generic over a string type,
in order to support all of `String`, `string_cache::Atom`, and
`gecko_string_cache::Atom`. Multiple trait bounds are used
for the various operations done with these strings.
One of these operations is creating a string (as efficiently as possible,
re-using an existing memory allocation if possible) from `Cow<str>`.
The `std::convert::From` trait seems natural for this, but
the relevant implementation was missing before this PR.
To work around this I’ve added a `FromCowStr` trait in `selectors`,
but with trait coherence that means one of `selectors` or `string_cache`
needs to depend on the other to implement this trait.
Using a trait from `std` would solve this.
The `Vec<T>` implementation is just added for consistency.
I also tried a more general
`impl<'a, O, B: ?Sized + ToOwned<Owned=O>> From<Cow<'a, B>> for O`,
but (the compiler thinks?) it conflicts with `From<T> for T` the impl
(after moving all of `collections::borrow` into `core::borrow`
to work around trait coherence).
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The new Vec::extend covers the duties of .extend_from_slice() and some
previous specializations.
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Specialize Vec::extend to Vec::extend_from_slice
I tried using the existing `SpecExtend` as a helper trait for this, but the instances would always conflict with the instances higher up in the file, so I created a new helper trait.
Benchmarking `extend` vs `extend_from_slice` with an slice of 1000 `u64`s gives the following results:
```
before:
running 2 tests
test tests::bench_extend_from_slice ... bench: 166 ns/iter (+/- 78)
test tests::bench_extend_trait ... bench: 1,187 ns/iter (+/- 697)
after:
running 2 tests
test tests::bench_extend_from_slice ... bench: 149 ns/iter (+/- 87)
test tests::bench_extend_trait ... bench: 138 ns/iter (+/- 70)
```
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Add Vec::dedup_by and Vec::dedup_by_key
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The show up separately in rustdoc.
This is a separate commit to keep the previous one’s diff shorter.
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These are displayed by rustdoc so should be correct.
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Fix some typos and improve doc comments style
r? @steveklabnik
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Documentation of what Default does for each type
Addresses #36265
I haven't changed the following types due to doubts:
1)src/libstd/ffi/c_str.rs
2)src/libcore/iter/sources.rs
3)src/libcore/hash/mod.rs
4)src/libcore/hash/mod.rs
5)src/librustc/middle/privacy.rs
r? @steveklabnik
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extend_with_element
Due to missing noalias annotations for &mut T in general (issue #31681),
in larger programs extend_from_slice and extend_with_element may both
compile very poorly. What is observed is that the .set_len() calls are
not lifted out of the loop, even for `Vec<u8>`.
Use a local length variable for the Vec length instead, and use a scope
guard to write this value back to self.len when the scope ends or on
panic. Then the alias analysis is easy.
This affects extend_from_slice, extend_with_element, the vec![x; n]
macro, Write impls for Vec<u8>, BufWriter, etc (but may / may not
have triggered since inlining can be enough for the compiler to get it right).
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This trait can be used to avoid the overhead of a fuse wrapper when an iterator
is already well-behaved.
Conforming to: RFC 1581
Closes: #35602
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Rollup of 23 pull requests
- Successful merges: #34370, #35415, #35595, #35610, #35613, #35614, #35621, #35660, #35663, #35670, #35671, #35672, #35681, #35686, #35690, #35695, #35707, #35708, #35713, #35722, #35725, #35726, #35731
- Failed merges: #35395
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Closes #35721
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Display all the remaining items of the iterator, similar to the `Debug`
implementation for `core::slice::Iter`:
https://github.com/rust-lang/rust/blob/f0bab98695f0a4877daabad9a5b0ba3e66121392/src/libcore/slice.rs#L930-L937
Using the `as_slice` method that was added in:
https://github.com/rust-lang/rust/pull/35447
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Similar to the `as_slice` method on `core::slice::Iter` struct.
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Make vec::Drain and binary_heap::Drain covariant
I removed all mutable pointers/references, and added covariance tests similar to the ones in #32635. It builds and passes the tests, but I noticed that there weren't any tests of Drain's behaviour (at least not in libcollectionstest), so I'm not sure if my changes accidently broke Drain's behaviour. Should I add some tests for that (and if so, what should the tests include)?
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Example was written in https://github.com/rust-lang/rust/pull/34911
Issue was brought up in this comment:
https://github.com/rust-lang/rust/commit/a005b2cd2ac679da7393e537aa05e2b7d32d36d5#commitcomment-18346958
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