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Can you make "somestr".trim_matches(char::is_ascii_punctuation) compile too ? it compiles with char::is_numeric #57307
Description
this works:
assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar"); //okbut this doesn't:
assert_eq!(
".,\"foo1bar\".,';".trim_matches(char::is_ascii_punctuation),
"foo1bar"
); //XXX fail
// expected signature of `fn(char) -> _`
// found signature of `for<'r> fn(&'r char) -> _`
// = note: required because of the requirements on the impl of `std::str::pattern::Pattern<'_>` for `for<'r> fn(&'r char) -> bool {std::char::methods::<impl char>::is_ascii_punctuation}`sig for is_numeric is:
pub fn is_numeric(self) -> boolAnd for is_ascii_punctuation is:
pub fn is_ascii_punctuation(&self) -> boolSo in order to make that work, I've had to do this:
pub trait Man {
fn manual_is_ascii_punctuation(self) -> bool;
}
impl Man for char {
#[inline]
fn manual_is_ascii_punctuation(self) -> bool {
self.is_ascii() && (self as u8).is_ascii_punctuation()
}
}
fn main() {
assert_eq!(
".,\"foo1bar\".,';".trim_matches(char::manual_is_ascii_punctuation),
"foo1bar"
); //works because the func sig matches
}Full code (playground):
#![allow(unused)]
pub trait Man {
fn manual_is_ascii_punctuation(self) -> bool;
}
impl Man for char {
#[inline]
fn manual_is_ascii_punctuation(self) -> bool {
self.is_ascii() && (self as u8).is_ascii_punctuation()
}
}
fn main() {
assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar"); //ok
assert_eq!(
".,\"foo1bar\".,';".trim_matches(char::manual_is_ascii_punctuation),
"foo1bar"
); //works because the func sig matches
assert_eq!(
".,\"foo1bar\".,';".trim_matches(char::is_ascii_punctuation),
"foo1bar"
); //XXX fail
// expected signature of `fn(char) -> _`
// found signature of `for<'r> fn(&'r char) -> _`
// = note: required because of the requirements on the impl of `std::str::pattern::Pattern<'_>` for `for<'r> fn(&'r char) -> bool {std::char::methods::<impl char>::is_ascii_punctuation}`
assert_eq!("\"123foo1bar\"".trim_matches(|x| x == '"'), "123foo1bar"); //ok
let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");
}Compiling playground v0.0.1 (/playground)
error[E0631]: type mismatch in function arguments
--> src/main.rs:22:29
|
22 | ".,\"foo1bar\".,';".trim_matches(char::is_ascii_punctuation),
| ^^^^^^^^^^^^
| |
| expected signature of `fn(char) -> _`
| found signature of `for<'r> fn(&'r char) -> _`
|
= note: required because of the requirements on the impl of `std::str::pattern::Pattern<'_>` for `for<'r> fn(&'r char) -> bool {std::char::methods::<impl char>::is_ascii_punctuation}`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0631`.
error: Could not compile `playground`.
To learn more, run the command again with --verbose.Reacted by Ossama Sybesma
Reacted by Ossama Sybesma
Activity
varkor commentedon Jan 3, 2019
You can just use a closure instead:
ExpHP commentedon Jan 3, 2019
Ouch. Looks like this is an unfortunate holdover from when these methods were a part of
std::ascii::AsciiExt.Technically speaking, I believe the answer is yes; this is technically possible. However, it cannot be done by implementing
PatternforF: FnMut(&char) -> bool, because that would overlap with the impl forF: FnMut(char) -> bool. There would have to be two impls that differ in a very subtle way:This unfortunate characteristic of these methods was mentioned on the PR that moved them, but I can't find any existing discussion on the possibility of adding
impl<'a> Pattern<'a> for fn(&char) -> bool.caemor commentedon Dec 8, 2020
Could we maybe change the documenation whenever char::is_aynthing is used to instead use the variant with the closure instead that is working for every (I only tried 2) char::is_anything function?
Benefit would be less confusion when mixing/trying the different char functions.
Disadvantage would be slightly longer (and therefore possible a bit more confusing?) documentation code.