This is a pretty major refactoring of the method dispatch infrastructure. It is intended to avoid gross inefficiencies and enable caching and other optimizations (e.g. #17995), though it itself doesn't seem to execute particularly faster yet. It also solves some cases where we were failing to resolve methods that we theoretically should have succeeded with.
Fixes#18674.
cc #18208
This commit deprecates the `_equiv` family of methods on `HashMap` and
`HashSet` by instead generalizing the "normal" methods like `get` and
`remove` to use the new `std::borrow` infrastructure.
[breaking-change]
Following [the collections reform
RFC](https://github.com/rust-lang/rfcs/pull/235),
this commit adds a new `borrow` module to libcore.
The module contains traits for borrowing data (`BorrowFrom` and
`BorrowFromMut`),
generalized cloning (`ToOwned`), and a clone-on-write smartpointer (`Cow`).
groundwork for better performance.
Key points:
- Separate out determining which method to use from actually selecting
a method (this should enable caching, as well as the pcwalton fast-reject strategy).
- Merge the impl selection back into method resolution and don't rely on
trait matching (this should perform better but also is needed to resolve some
kind of conflicts, see e.g. `method-two-traits-distinguished-via-where-clause.rs`)
- Purge a lot of out-of-date junk and coercions from method lookups.
This breaks code that referred to variant names in the same namespace as
their enum. Reexport the variants in the old location or alter code to
refer to the new locations:
```
pub enum Foo {
A,
B
}
fn main() {
let a = A;
}
```
=>
```
pub use self::Foo::{A, B};
pub enum Foo {
A,
B
}
fn main() {
let a = A;
}
```
or
```
pub enum Foo {
A,
B
}
fn main() {
let a = Foo::A;
}
```
[breaking-change]
This breaks code that referred to variant names in the same namespace as
their enum. Reexport the variants in the old location or alter code to
refer to the new locations:
```
pub enum Foo {
A,
B
}
fn main() {
let a = A;
}
```
=>
```
pub use self::Foo::{A, B};
pub enum Foo {
A,
B
}
fn main() {
let a = A;
}
```
or
```
pub enum Foo {
A,
B
}
fn main() {
let a = Foo::A;
}
```
[breaking-change]
creating a new Id object requires the format to match a subset of `ID` format defined by the DOT language. When the format did not match, the function called assert. This was not mentioned in the docs or the spec. I made the failure explicit by returning an Result<Id, ()>.
`slice_shift_char` splits a `str` into it's leading `char` and the remainder
of the `str`. Currently, it returns a `(Option<char>, &str)` such that:
"bar".slice_shift_char() => (Some('b'), "ar")
"ar".slice_shift_char() => (Some('a'), "r")
"r".slice_shift_char() => (Some('r'), "")
"".slice_shift_char() => (None, "")
This is a little odd. Either a `str` can be split into both a head and a
tail or it cannot. So the return type should be `Option<(char, &str)>`.
With the current behaviour, in the case of the empty string, the `str`
returned is meaningless - it is always the empty string.
This commit changes slice_shift_char so that:
"bar".slice_shift_char() => Some(('b', "ar"))
"ar".slice_shift_char() => Some(('a', "r"))
"r".slice_shift_char() => Some(('r', ""))
"".slice_shift_char() => None
[breaking-change]
"_" should keep the default syntax class (symbol, not word). This
allows, e.g., `forward-word' to behave in the familiar way, jumping to
underscores within a function or variable name.
Fix for task in Metabug #18009 (Rebased version of https://github.com/rust-lang/rust/pull/18170)
This changes much of about how RingBuf functions. `lo`, `nelts` are replaced by a more traditional `head` and`tail`. The `Vec<Option<T>>` is replaced by a bare pointer that is managed by the `RingBuf` itself. This also expects the ring buffer to always be size that is a power of 2.
This change also includes a number of new tests to cover the some areas that could be of concern with manual memory management.
The benchmarks have been reworked since the old ones were benchmarking of the Ring buffers growth rather then the actual test.
The unit test suite have been expanded, and exposed some bugs in `fn get()` and `fn get_mut()`
## Benchmark
**Before:**
```
test ring_buf::tests::bench_grow_1025 ... bench: 8919 ns/iter (+/- 87)
test ring_buf::tests::bench_iter_1000 ... bench: 924 ns/iter (+/- 28)
test ring_buf::tests::bench_mut_iter_1000 ... bench: 918 ns/iter (+/- 6)
test ring_buf::tests::bench_new ... bench: 15 ns/iter (+/- 0)
test ring_buf::tests::bench_pop_100 ... bench: 294 ns/iter (+/- 9)
test ring_buf::tests::bench_pop_front_100 ... bench: 948 ns/iter (+/- 32)
test ring_buf::tests::bench_push_back_100 ... bench: 291 ns/iter (+/- 16)
test ring_buf::tests::bench_push_front_100 ... bench: 311 ns/iter (+/- 27
```
**After:**
```
test ring_buf::tests::bench_grow_1025 ... bench: 2209 ns/iter (+/- 169)
test ring_buf::tests::bench_iter_1000 ... bench: 534 ns/iter (+/- 27)
test ring_buf::tests::bench_mut_iter_1000 ... bench: 515 ns/iter (+/- 28)
test ring_buf::tests::bench_new ... bench: 11 ns/iter (+/- 0)
test ring_buf::tests::bench_pop_100 ... bench: 170 ns/iter (+/- 5)
test ring_buf::tests::bench_pop_front_100 ... bench: 171 ns/iter (+/- 11)
test ring_buf::tests::bench_push_back_100 ... bench: 172 ns/iter (+/- 13)
test ring_buf::tests::bench_push_front_100 ... bench: 158 ns/iter (+/- 12)
```
