implement `From<Vec<char>>` and `From<&'a [char]>` for `String`
Though there are ways to convert a slice or vec of chars into a string,
it would be nice to be able to just do `String::from(&['a', 'b', 'c'])`,
so this PR implements `From<Vec<char>>` and `From<&'a [char]>` for
String.
Escape fewer Unicode codepoints in `Debug` impl of `str`
Use the same procedure as Python to determine whether a character is
printable, described in [PEP 3138]. In particular, this means that the
following character classes are escaped:
- Cc (Other, Control)
- Cf (Other, Format)
- Cs (Other, Surrogate), even though they can't appear in Rust strings
- Co (Other, Private Use)
- Cn (Other, Not Assigned)
- Zl (Separator, Line)
- Zp (Separator, Paragraph)
- Zs (Separator, Space), except for the ASCII space `' '` `0x20`
This allows for user-friendly inspection of strings that are not
English (e.g. compare `"\u{e9}\u{e8}\u{ea}"` to `"éèê"`).
Fixes#34318.
CC #34422.
[PEP 3138]: https://www.python.org/dev/peps/pep-3138/
Make vec::Drain and binary_heap::Drain covariant
I removed all mutable pointers/references, and added covariance tests similar to the ones in #32635. It builds and passes the tests, but I noticed that there weren't any tests of Drain's behaviour (at least not in libcollectionstest), so I'm not sure if my changes accidently broke Drain's behaviour. Should I add some tests for that (and if so, what should the tests include)?
Though there are ways to convert a slice or vec of chars into a string,
it would be nice to be able to just do `String::from(['a', 'b', 'c'])`,
so this PR implements `From<Vec<char>>` and `From<&'a [char]>` for
String.
Doc example improvements for `slice::windows`.
* Modify existing example to not rely on printing to see results
* Add an example demonstrating when slice is shorter than `size`
feat: reinterpret `precision` field for strings
This commit changes the behavior of formatting string arguments with both width and precision fields set.
Documentation says that the `width` field is the "minimum width" that the format should take up. If the value's string does not fill up this many characters, then the padding specified by fill/alignment will be used to take up the required space.
This is true for all formatted types except string, which is truncated down to `precision` number of chars and then all of `fill`, `align` and `width` fields are completely ignored.
For example: `format!("{:/^10.8}", "1234567890);` emits "12345678". In the contrast Python version works as the expected:
```python
>>> '{:/^10.8}'.format('1234567890')
'/12345678/'
```
This commit gives back the `Python` behavior by changing the `precision` field meaning to the truncation and nothing more. The result string *will* be prepended/appended up to the `width` field with the proper `fill` char.
__However, this is the breaking change, I admit.__ Feel free to close it, but otherwise it should be mentioned in the `std::fmt` documentation somewhere near of `fill/align/width` fields description.
implement AddAssign for String
Currently `String` implements `Add` but not `AddAssign`. This PR fills in that gap.
I played around with having `AddAssign` (and `Add` and `push_str`) take `AsRef<str>` instead of `&str`, but it looks like that breaks arguments that implement `Deref<Target=str>` and not `AsRef<str>`. Comments in [`libcore/convert.rs`](https://github.com/rust-lang/rust/blob/master/src/libcore/convert.rs#L207-L213) make it sound like we could fix this with a blanket impl eventually. Does anyone know what's blocking that?
