core: add likely and unlikely intrinsics
I'm no good at reading assembly, but I have tried a stage1 compiler with this patch, and it does cause different asm output. Additionally, testing this compiler on my httparse crate with some `likely` usage added in to the branches does affect benchmarks. However, I'm sure a codegen test should be included, if anyone knows what it should look like.
There isn't an entry in `librustc_trans/context.rs` in this diff, because it already exists (`llvm.expect.i1` is used for array indices).
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Even though this does affect httparse benchmarks, it doesn't seem to affect it the same way GCC's `__builtin_expect` affects picohttpparser. I was confused that the deviation on the benchmarks grew hugely when testing this, especially since I'm absolutely certain that the branchs where I added `likely` were always `true`. I chalk that up to GCC and LLVM handle branch prediction differently.
cc #26179
Introduce max_by/min_by on iterators
See https://github.com/rust-lang/rfcs/issues/1722 for reference.
It seems that there is `min`, `max` (simple computation of min/max), `min_by_key`, `max_by_key` (min/max by comparing mapped values) but no `min_by` and `max_by` (min/max according to comparison function). However, e.g. on vectors or slices there is `sort`, `sort_by_key` and `sort_by`.
Document try!'s error conversion behaviour
try!'s documentation currently doesn't document the error conversion behaviour of the macro. This patch extends the documentation.
Open questions:
* is it worthwhile to have seperate examples with and without wrapping behaviour? It's not immediately obvious that From<T> for T is always defined. Though this is necessary for the macro to work in any case, is this the place to expect that knowledge.
Implement std::convert traits for char
This is motivated by avoiding the `as` operator, which sometimes silently truncates, and instead use conversions that are explicitly lossless and infallible.
I’m less certain that `From<u8> for char` should be implemented: while it matches an existing behavior of `as`, it’s not necessarily the right thing to use for non-ASCII bytes. It effectively decodes bytes as ISO/IEC 8859-1 (since Unicode designed its first 256 code points to be compatible with that encoding), but that is not apparent in the API name.
add evocative examples for `BitOr` and `BitXor`
These are exactly equivalent to PR #35809, with one caveat: I do not believe there is a non-bitwise binary XOR operator in Rust, so here it's expressed as `(a || b) && !(a && b)`.
Alternative decompositions are `(a && !b) || (!a && b)` and `(a || b) && (!a || !b)`. Let me know if you think one of those would be clearer.
r? @GuillaumeGomez
accumulate vector and assert for RangeFrom and RangeInclusive examples
PR #35695 for `Range` was merged, so it seems that this side-effect-free style is preferred for Range* examples. This PR performs the same translation for `RangeFrom` and `RangeInclusive`. It also removes what looks to be an erroneously commented line for `#![feature(step_by)]`, and an unnecessary primitive-type annotation in `0u8..`.
These are exactly equivalent to PR #35809, with one caveat: I do not believe there is a non-bitwise binary "xor" operator in Rust, so here it's expressed as (a || b) && !(a && b).
r? @GuillaumeGomez
improved documentation a la PR #35993
improve `BitAnd` trait documentation
This pull request is based on the discussion in PR #35927.
Add a module-level note that `&&` and `||` are short-circuiting operators and not overloadable.
Add a simple `Scalar` example that lifts the `&` operator to a trivial struct tuple.
Make `BooleanVector` a struct tuple.
Derive `PartialEq` for `BooleanVector` instead of implementing it.
Adds a `fn main` wrapper so that the example can integrate with Rust Playground.
improve documentation for `Fn*` traits
This PR is not yet a serious attempt at contribution. Rather, I'm opening this for discussion. I can think of a few things we may want to accomplish with the documentation of the `Fn`, `FnMut`, and `FnOnce` traits:
- the relationship between these traits and the closures that implement them
- examples of non-closure implementations
- the relationship between these traits and Rust's ownership semantics
show how iterating over `RangeTo` and `RangeToInclusive` fails
Feedback on PR #35701 seems to be positive, so this does the same thing for `RangeTo` and `RangeToInclusive`.
These fit with other From implementations between integer types.
This helps the coding style of avoiding the 'as' operator that sometimes
silently truncates, and signals that these specific conversions are
lossless and infaillible.
This pull request is based on the discussion in PR #35927.
Add a module-level note that `&&` and `||` are short-circuiting operators and not overloadable.
Add a simple `Scalar` example that lifts the `&` operator to a trivial struct tuple.
Make `BooleanVector` a struct tuple.
Derive `PartialEq` for `BooleanVector` instead of implementing it.
Adds a `fn main` wrapper so that the example can integrate with Rust Playground.
simplified bitand expression
add a comment explaining what "rhs" means
PR #35695 for `Range` was approved, so it seems that this side-effect-free style is preferred for Range* examples. This PR performs the same translation for `RangeFrom` and `RangeInclusive`. It also removes what looks to be an erroneously commented line for `#![feature(step_by)]`, and an unnecessary primitive-type annotation in `0u8..`.
add `fn main` wrappers to enable Rust Playground "Run" button
