This commit introduces 2 methods - `Option::zip` and `Option::zip_with` with
respective signatures:
- zip: `(Option<T>, Option<U>) -> Option<(T, U)>`
- zip_with: `(Option<T>, Option<U>, (T, U) -> R) -> Option<R>`
Both are under the feature gate "option_zip".
I'm not sure about the name "zip", maybe we can find a better name for this.
(I would prefer `union` for example, but this is a keyword :( )
--------------------------------------------------------------------------------
Recently in a russian rust begginers telegram chat a newbie asked (translated):
> Are there any methods for these conversions:
>
> 1. `(Option<A>, Option<B>) -> Option<(A, B)>`
> 2. `Vec<Option<T>> -> Option<Vec<T>>`
>
> ?
While second (2.) is clearly `vec.into_iter().collect::<Option<Vec<_>>()`, the
first one isn't that clear.
I couldn't find anything similar in the `core` and I've come to this solution:
```rust
let tuple: (Option<A>, Option<B>) = ...;
let res: Option<(A, B)> = tuple.0.and_then(|a| tuple.1.map(|b| (a, b)));
```
However this solution isn't "nice" (same for just `match`/`if let`), so I thought
that this functionality should be in `core`.
make `mem::discriminant` const
implements #69821, which could be used as a tracking issue for `const_discriminant`.
Should this be added to the meta tracking issue #57563?
@Lokathor
Stabilize const for integer {to,from}_{be,le,ne}_bytes methods
All of these functions can be implemented simply and naturally as const functions, e.g. `u32::from_le_bytes` can be implemented as
```rust
(bytes[0] as u32)
| (bytes[1] as u32) << 8
| (bytes[2] as u32) << 16
| (bytes[3] as u32) << 24
```
So stabilizing the constness will not expose that internally they are implemented using transmute which is not const in stable.
Remove spotlight
I had a few comments saying that this feature was at best misunderstood or not even used so I decided to organize a poll about on [twitter](https://twitter.com/imperioworld_/status/1232769353503956994). After 87 votes, the result is very clear: it's not useful. Considering the amount of code we have just to run it, I think it's definitely worth it to remove it.
r? @kinnison
cc @ollie27
Stabilize assoc_int_consts associated int/float constants
The next step in RFC https://github.com/rust-lang/rfcs/pull/2700 (tracking issue #68490). Stabilizing the associated constants that were added in #68325.
* Stabilize all constants under the `assoc_int_consts` feature flag.
* Update documentation on old constants to say they are soft-deprecated and the new ones should be preferred.
* Update documentation examples to use new constants.
* Remove `uint_macro` and use `int_macro` for all integer types since the macros were identical anyway.
r? @LukasKalbertodt
Add primitive module to libcore
This re-exports the primitive types from libcore at `core::primitive` to allow
macro authors to have a reliable location to use them from.
Fixes#44865
All of these functions can be implemented simply and naturally as
const functions, e.g. u32::from_le_bytes can be implemented as
(bytes[0] as u32)
| (bytes[1] as u32) << 8
| (bytes[2] as u32) << 16
| (bytes[3] as u32) << 24
So stabilizing the constness will not expose that internally they are
implemented using transmute which is not const in stable.
Make integer exponentiation methods unstably const
cc #53718
This makes the following inherent methods on integer primitives into unstable `const fn`:
- `pow`
- `checked_pow`
- `wrapping_pow`
- `overflowing_pow`
- `saturating_pow`
- `next_power_of_two`
- `checked_next_power_of_two`
- `wrapping_next_power_of_two`
Only two changes were made to the implementation of these methods. First, I had to switch from the `?` operator, which is not yet implemented in a const context, to a `try_opt` macro. Second, `next_power_of_two` was using `ops::Add::add` (see the first commit) to "get overflow checks", so I switched to `#[rustc_inherit_overflow_checks]`. I'm not quite sure why the attribute wasn't used in the first place.
Step stage0 to bootstrap from 1.42
This also includes a commit which fixes the rustfmt downloading logic to redownload when the rustfmt channel changes, and bumps rustfmt to a more recent version.
This flag opts out of the min-const-fn checks entirely, which is usually
not what we want. The few cases where the flag is still necessary have
been annotated.
