Add Derive not possible question to Copy
This adds a question and answer to the Q&A section of the Copy
docs. Specifically, it asks the question I asked while reading
the docs, and gives its answer.
cc @steveklabnik
This adds a question and answer to the Q&A section of the Copy
docs. Specifically, it asks the question I asked while reading
the docs, and gives its answer.
Add non-panicking abs() functions to all signed integer types.
Currently, calling abs() on one of the signed integer types might panic (in
debug mode at least) because the absolute value of the largest negative value
can not be represented in that signed type. Unlike all other integer
operations, there is currently not a non-panicking version on this function.
This seems to just be an oversight in the design, therefore just adding it now.
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/
Currently, calling abs() on one of the signed integer types might panic (in
debug mode at least) because the absolute value of the largest negative value
can not be represented in that signed type. Unlike all other integer
operations, there is currently not a non-panicking version on this function.
This seems to just be an oversight in the design, therefore just adding it now.
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.
[PEP 3138]: https://www.python.org/dev/peps/pep-3138/
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.
core: impl From<T> for Option<T>
First, the semantics of this `impl` seem spot on. If I have a value `T`, and I wish to make a `Option<T>`, then `Option::from(val)` should always give `Some(val)`.
Second, this allows improvement for several APIs that currently take `Option<T>` as arguments. Consider:
```rust
fn set_read_timeout(&mut self, timeout: Option<u32>) {
// ...
}
x.set_read_timeout(Some(30));
x.set_read_timeout(Some(10));
x.set_read_timeout(None);
```
With this `impl`:
```rust
fn set_read_timeout<T: Into<Option<u32>>>(&mut self, timeout: T) {
let timeout = timeout.into();
// ...
}
x.set_read_timeout(30);
x.set_read_timeout(10);
x.set_read_timeout(Some(10)); // backwards compatible
x.set_read_timeout(None);
```
The change to those methods aren't included, but could be modified later.
r? @sfackler
Fix up documentation around no_std
1. Fix the sections in the book to have the correct signatures. I've
also marked them as `ignore`; there's no way to set the `no_std`
feature for libc, so it pulls in the stdlib, so this wasn't even
testing the actual thing it was testing. Better to just ignore.
2. Correcting libcore's docs for factual inaccuracy, and add a note
about language items.
Fixes#33677
r? @alexcrichton
1. Fix the sections in the book to have the correct signatures. I've
also marked them as `ignore`; there's no way to set the `no_std`
feature for libc, so it pulls in the stdlib, so this wasn't even
testing the actual thing it was testing. Better to just ignore.
2. Correcting libcore's docs for factual inaccuracy, and add a note
about language items.
Fixes#33677
doc: Mention that writeln! and println! always use LF
Fixes#34697
I'm not really satisfied with the wording, but I didn't have a better idea. Suggestions welcome.
