Optimized string FromIterator + Extend impls
I noticed that there was a lost opportunity to reuse string buffers in `FromIterator<String>` and `FromIterator<Cow<str>>`; updated the implementations to use these. In practice this translates to at least one fewer allocation when using these APIs.
Additionally, rewrote `Extend` implementations to use `iter.for_each`, which (supposedly) helps the compiler optimize those loops (because iterator adapters are encouraged to provide optimized implementations of `fold` and `try_fold`.
Add Weak.ptr_eq
I hope the doc tests alone are good enough.
We also might want to discuss the dangling pointer case (from `Weak::new()`).
Updates #55981.
Assorted tweaks
- preallocate `VecDeque` in `Decodable::decode` (as it is done with other collections which can do it)
- add a FIXME to `String::from_utf16`
r? @RalfJung
Doc total order requirement of sort(_unstable)_by
I took the definition of what a total order is from the Ord trait
docs. I specifically put "elements of the slice" because if you
have a slice of f64s, but know none are NaN, then sorting by
partial ord is total in this case. I'm not sure if I should give
such an example in the docs or not.
r? @GuillaumeGomez
Speed up String::from_utf16
Collecting into a `Result` is idiomatic, but not necessarily fast due to rustc not being able to preallocate for the resulting collection. This is fine in case of an error, but IMO we should optimize for the common case, i.e. a successful conversion.
This changes the behavior of `String::from_utf16` from collecting into a `Result` to pushing to a preallocated `String` in a loop.
According to [my simple benchmark](https://gist.github.com/ljedrz/953a3fb74058806519bd4d640d6f65ae) this change makes `String::from_utf16` around **twice** as fast.
global allocators: add a few comments
These comments answer some questions that came up when I tried to understand how the control flow works for the global allocator, `Global` and `System`.
r? @alexcrichton
string: Add documentation for `From` impls
Hi this is part of #51430. I'm a first time contributor, so I started with a small task adding a bit of documentation for From impls.
This commit deletes the `alloc_system` crate from the standard
distribution. This unstable crate is no longer needed in the modern
stable global allocator world, but rather its functionality is folded
directly into the standard library. The standard library was already the
only stable location to access this crate, and as a result this should
not affect any stable code.
This commit removes all jemalloc related submodules, configuration, etc,
from the bootstrap, from the standard library, and from the compiler.
This will be followed up with a change to use jemalloc specifically as
part of rustc on blessed platforms.
