Fixes#83046
The program
fn main() {
println!("{:?}", '"');
println!("{:?}", "'");
}
would previously print
'\"'
"\'"
With this patch it now prints:
'"'
"'"
`escape_unicode`, `escape_default`, `len_utf8`, `len_utf16`, to_ascii_lowercase`, `eq_ignore_ascii_case`
`u8` methods `to_ascii_lowercase`, `to_ascii_uppercase` also must be made const
u8 methods made const
Update methods.rs
Update mod.rs
Update methods.rs
Fix `since` in rustc_const_stable to next stable
Fix `since` in rustc_const_stable to next stable
Update methods.rs
Update mod.rs
Slight perf improvement on char::to_ascii_lowercase
`char::to_ascii_lowercase()` was checking if it was ascii and then if it was in the right range. Instead propose to check once (I think removing a compare and a shift in the process: [godbolt](https://godbolt.org/z/e5Tora) ).
before:
```
test char::methods::bench_to_ascii_lowercase ... bench: 11,196 ns/iter (+/- 632)
test char::methods::bench_to_ascii_uppercase ... bench: 11,656 ns/iter (+/- 671)
```
after:
```
test char::methods::bench_to_ascii_lowercase ... bench: 9,612 ns/iter (+/- 979)
test char::methods::bench_to_ascii_uppercase ... bench: 8,241 ns/iter (+/- 701)
```
(calling u8::to_ascii_lowercase and letting that flip the 5th bit is also an option, but it's more instructions. I'm thinking for things around ascii and char we want to be as efficient as possible.)
Implement From<char> for u64 and u128.
With this PR you can write
```
let u = u64::from('👤');
let u = u128::from('👤');
```
Previously, you could already write `as` conversions ([Playground link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=cee18febe28e69024357d099f07ca081)):
```
// Lossless conversions
dbg!('👤' as u32); // Prints 128100
dbg!('👤' as u64); // Prints 128100
dbg!('👤' as u128); // Prints 128100
// truncates, thus no `From` impls.
dbg!('👤' as u8); // Prints 100
dbg!('👤' as u16); // Prints 62564
// These `From` impls already exist.
dbg!(u32::from('👤')); // Prints 128100
dbg!(u64::from(u32::from('👤'))); // Prints 128100
```
The idea is from ``@gendx`` who opened [this Internals thread](https://internals.rust-lang.org/t/implement-from-char-for-u64/13454), and ``@withoutboats`` responded that someone should open a PR for it.
Some people mentioned `From<char>` impls for `f32` and `f64`, but that doesn't seem correct to me, so I didn't include them here.
I don't know what the feature should be named. Must it be registered somewhere, like unstable features?
r? ``@withoutboats``
