Ensures that the same error type is propagated throughout. Unnecessary leakage
of the internals is prevented through the usage of stability attributes.
Closes#24748
Ensures that the same error type is propagated throughout. Unnecessary leakage
of the internals is prevented through the usage of stability attributes.
Closes#24748
These implementations were intended to be unstable, but currently the stability
attributes cannot handle a stable trait with an unstable `impl` block. This
commit also audits the rest of the standard library for explicitly-`#[unstable]`
impl blocks. No others were removed but some annotations were changed to
`#[stable]` as they're defacto stable anyway.
One particularly interesting `impl` marked `#[stable]` as part of this commit
is the `Add<&[T]>` impl for `Vec<T>`, which uses `push_all` and implicitly
clones all elements of the vector provided.
Closes#24791
[breaking-change]
These implementations were intended to be unstable, but currently the stability
attributes cannot handle a stable trait with an unstable `impl` block. This
commit also audits the rest of the standard library for explicitly-`#[unstable]`
impl blocks. No others were removed but some annotations were changed to
`#[stable]` as they're defacto stable anyway.
One particularly interesting `impl` marked `#[stable]` as part of this commit
is the `Add<&[T]>` impl for `Vec<T>`, which uses `push_all` and implicitly
clones all elements of the vector provided.
Closes#24791
This commit brings the `Error` trait in line with the [Error interoperation
RFC](https://github.com/rust-lang/rfcs/pull/201) by adding downcasting,
which has long been intended. This change means that for any `Error`
trait objects that are `'static`, you can downcast to concrete error
types.
To make this work, it is necessary for `Error` to inherit from
`Reflect` (which is currently used to mark concrete types as "permitted
for reflection, aka downcasting"). This is a breaking change: it means
that impls like
```rust
impl<T> Error for MyErrorType<T> { ... }
```
must change to something like
```rust
impl<T: Reflect> Error for MyErrorType<T> { ... }
```
except that `Reflect` is currently unstable (and should remain so for
the time being). For now, code can instead bound by `Any`:
```rust
impl<T: Any> Error for MyErrorType<T> { ... }
```
which *is* stable and has `Reflect` as a super trait. The downside is
that this imposes a `'static` constraint, but that only
constrains *when* `Error` is implemented -- it does not actually
constrain the types that can implement `Error`.
[breaking-change]
These are useful when you want to catch the signals, like when you're making a kernel, or if you just don't want the overhead. (I don't know if there are any of the second kind of people, I don't think it's a good idea, but hey, choice is good).
Currently, LLVM lowers a cttz8 on x86_64 to these instructions:
```asm
movzbl %dil, %eax
bsfl %eax, %eax
movl $32, %ecx
cmovnel %eax, %ecx
cmpl $32, %ecx
movl $8, %eax
cmovnel %ecx, %eax
```
To improve the codegen, we can zero extend the 8 bit integer, then set
bit 8 and perform a cttz operation on the extended value. That way
there's no conditional operation involved at all.
This was discovered by this benchmark: https://github.com/Kimundi/long_strings_without_repeats
Timings on my box with the current nightly:
```
running 4 tests
test bench_cpp_naive_big ... bench: 5479222 ns/iter (+/- 254222)
test bench_noop_big ... bench: 571405 ns/iter (+/- 111950)
test bench_rust_naive_big ... bench: 7798102 ns/iter (+/- 148841)
test bench_rust_unsafe_big ... bench: 6606488 ns/iter (+/- 67529)
```
Timings with the patch applied:
```
running 4 tests
test bench_cpp_naive_big ... bench: 5470944 ns/iter (+/- 7109)
test bench_noop_big ... bench: 568944 ns/iter (+/- 6895)
test bench_rust_naive_big ... bench: 6795901 ns/iter (+/- 43806)
test bench_rust_unsafe_big ... bench: 5584879 ns/iter (+/- 5291)
```
```asm
movzbl %dil, %eax
bsfl %eax, %eax
movl $32, %ecx
cmovnel %eax, %ecx
cmpl $32, %ecx
movl $8, %eax
cmovnel %ecx, %eax
```
which has some unnecessary overhead, having two conditional moves.
To improve the codegen, we can zero extend the 8 bit integer, then set
bit 8 and perform a cttz operation on the extended value. That way
there's no conditional operation involved at all.
core: Fix size_hint for signed integer `Range<T>` iterators
There was an overflow bug in .size_hint() for signed iterators, which
produced an hilariously incorrect size or an overflow panic.
Incorrect size is a serious bug since the iterators are marked
ExactSizeIterator. (And leads to abort() on (-1i8..127).collect() when
the collection tries to preallocate too much).
> (-1i8..127).size_hint()
(18446744073709551488, Some(18446744073709551488))
Bug found using quickcheck.
Fixes#24851
Instead of using the O(n) defaults, define O(1) shortcuts. I also copied (and slightly modified) the relevant tests from the iter tests into the slice tests just in case someone comes along and changes them in the future.
Partially implements #24214.
There was an overflow bug in .size_hint() for signed iterators, which
produced an hilariously incorrect size or an overflow panic.
Incorrect size is a serious bug since the iterators are marked
ExactSizeIterator. (And leads to abort() on (-1i8..127).collect() when
the collection tries to preallocate too much).
All signed range iterators were affected.
> (-1i8..127).size_hint()
(18446744073709551488, Some(18446744073709551488))
Bug found using quickcheck.
Fixes#24851
These new intrinsics are comparable to `atomic_signal_fence` in C++,
ensuring the compiler will not reorder memory accesses across the
barrier, nor will it emit any machine instructions for it.
Closes#24118, implementing RFC 888.
1. Use next_back for last.
2. Use slices for computing nth. It might be possible to use the same
code for both the mut/const case but I don't know how that will play
with compiler optimizations.
This is an implementation of [RFC 1030][rfc] which adds these traits to the
prelude and additionally removes all inherent `into_iter` methods on collections
in favor of the trait implementation (which is now accessible by default).
[rfc]: https://github.com/rust-lang/rfcs/pull/1030
This is technically a breaking change due to the prelude additions and removal
of inherent methods, but it is expected that essentially no code breaks in
practice.
[breaking-change]
Closes#24538
as accepted in [RFC 526](https://github.com/rust-lang/rfcs/blob/master/text/0526-fmt-text-writer.md).
Note that this brand new method is marked as **stable**. I judged this safe enough: it’s simple enough that it’s very unlikely to change. Still, I can mark it unstable instead if you prefer.
r? @alexcrichton
This commit removes all the old casting/generic traits from `std::num` that are
no longer in use by the standard library. This additionally removes the old
`strconv` module which has not seen much use in quite a long time. All generic
functionality has been supplanted with traits in the `num` crate and the
`strconv` module is supplanted with the [rust-strconv crate][rust-strconv].
[rust-strconv]: https://github.com/lifthrasiir/rust-strconv
This is a breaking change due to the removal of these deprecated crates, and the
alternative crates are listed above.
[breaking-change]
