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#![cfg_attr(feature = "nightly", feature(pattern))] use std::borrow::Cow; /// This trait is a shim for the required functionality /// normally provided directly by [`std::str::pattern::Pattern`] /// (which is currently unstable). /// /// On stable Rust it's implemented on the same standard types as /// [`std::str::pattern::Pattern`], but on nightly you can enable /// a `"nightly"` feature and any custom types implementing /// [`std::str::pattern::Pattern`] will be supported as well. pub trait Pattern<'s> { /// This will always be [`std::str::MatchIndices<'s, /// Self>`](std::str::MatchIndices) but we can't spell it out because it /// requires `Self: `[`std::str::pattern::Pattern`] and that trait bound is /// currently unstable and can't be written in a stable Rust. type MatchIndices: Iterator<Item = (usize, &'s str)>; /// A wrapper for [`&str::match_indices`] with a given pattern. fn match_indices_in(self, s: &'s str) -> Self::MatchIndices; } macro_rules! impl_pattern { ($ty:ty $(where $($bound:tt)*)?) => { impl<'s $(, $($bound)*)?> Pattern<'s> for $ty { type MatchIndices = std::str::MatchIndices<'s, Self>; fn match_indices_in(self, s: &'s str) -> Self::MatchIndices { s.match_indices(self) } } }; } #[cfg(not(feature = "nightly"))] const _: () = { impl_pattern!(char); impl_pattern!(&str); impl_pattern!(&String); impl_pattern!(&[char]); impl_pattern!(&&str); impl_pattern!(F where F: FnMut(char) -> bool); }; #[cfg(feature = "nightly")] impl_pattern!(P where P: std::str::pattern::Pattern<'s>); /// Some [`str`] methods perform destructive transformations and so /// return [`String`] even when no modification is necessary. /// /// This helper trait provides drop-in variants of such methods, but /// instead avoids allocations when no modification is necessary. /// /// For now only implemented for [`&str`](str) and returns /// [`Cow<str>`](std::borrow::Cow), but in the future might be extended /// to other types. pub trait CowUtils<'s> { type Output; /// Replaces all matches of a pattern with another string. fn cow_replace(self, pattern: impl Pattern<'s>, to: &str) -> Self::Output; /// Replaces first N matches of a pattern with another string. fn cow_replacen(self, from: impl Pattern<'s>, to: &str, count: usize) -> Self::Output; /// Returns a copy of this string where each character is mapped to its /// ASCII lower case equivalent. fn cow_to_ascii_lowercase(self) -> Self::Output; /// Returns the lowercase equivalent of this string slice. fn cow_to_lowercase(self) -> Self::Output; /// Returns a copy of this string where each character is mapped to its /// ASCII upper case equivalent. fn cow_to_ascii_uppercase(self) -> Self::Output; /// Returns the uppercase equivalent of this string slice. fn cow_to_uppercase(self) -> Self::Output; } unsafe fn cow_replace<'s>( src: &'s str, match_indices: impl Iterator<Item = (usize, &'s str)>, to: &str, ) -> Cow<'s, str> { let mut result = Cow::default(); let mut last_start = 0; for (index, matched) in match_indices { result += src.get_unchecked(last_start..index); if !to.is_empty() { result.to_mut().push_str(to); } last_start = index + matched.len(); } result += src.get_unchecked(last_start..); result } impl<'s> CowUtils<'s> for &'s str { type Output = Cow<'s, str>; /// This is similar to [`str::replace`](https://doc.rust-lang.org/std/primitive.str.html#method.replace), but returns /// a slice of the original string when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("abc".cow_replace("def", "ghi"), Cow::Borrowed("abc")); /// assert_matches!("$$str$$".cow_replace("$", ""), Cow::Borrowed("str")); /// assert_matches!("aaaaa".cow_replace("a", ""), Cow::Borrowed("")); /// assert_matches!("abc".cow_replace("b", "d"), Cow::Owned(s) if s == "adc"); /// assert_matches!("$a$b$".cow_replace("$", ""), Cow::Owned(s) if s == "ab"); /// ``` fn cow_replace(self, pattern: impl Pattern<'s>, to: &str) -> Self::Output { unsafe { cow_replace(self, pattern.match_indices_in(self), to) } } /// This is similar to [`str::replacen`](https://doc.rust-lang.org/std/primitive.str.html#method.replacen), but returns /// a slice of the original string when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("abc".cow_replacen("def", "ghi", 10), Cow::Borrowed("abc")); /// assert_matches!("$$str$$".cow_replacen("$", "", 2), Cow::Borrowed("str$$")); /// assert_matches!("$a$b$".cow_replacen("$", "", 1), Cow::Borrowed("a$b$")); /// assert_matches!("aaaaa".cow_replacen("a", "", 10), Cow::Borrowed("")); /// assert_matches!("aaaaa".cow_replacen("a", "b", 0), Cow::Borrowed("aaaaa")); /// assert_matches!("abc".cow_replacen("b", "d", 1), Cow::Owned(s) if s == "adc"); /// ``` fn cow_replacen(self, pattern: impl Pattern<'s>, to: &str, count: usize) -> Self::Output { unsafe { cow_replace(self, pattern.match_indices_in(self).take(count), to) } } /// This is similar to [`str::to_ascii_lowercase`](https://doc.rust-lang.org/std/primitive.str.html#method.to_ascii_lowercase), but returns /// original slice when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("abcd123".cow_to_ascii_lowercase(), Cow::Borrowed("abcd123")); /// assert_matches!("ὀδυσσεύς".cow_to_ascii_lowercase(), Cow::Borrowed("ὀδυσσεύς")); /// assert_matches!("ὈΔΥΣΣΕΎΣ".cow_to_ascii_lowercase(), Cow::Borrowed("ὈΔΥΣΣΕΎΣ")); /// assert_matches!("AbCd".cow_to_ascii_lowercase(), Cow::Owned(s) if s == "abcd"); /// ``` fn cow_to_ascii_lowercase(self) -> Self::Output { match self.as_bytes().iter().position(u8::is_ascii_uppercase) { Some(pos) => { let mut output = self.to_owned(); // We already know position of the first uppercase char, // so no need to rescan the part before it. unsafe { output.get_unchecked_mut(pos..) }.make_ascii_lowercase(); Cow::Owned(output) } None => Cow::Borrowed(self), } } /// This is similar to [`str::to_lowercase`](https://doc.rust-lang.org/std/primitive.str.html#method.to_lowercase), but returns /// original slice when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("abcd123".cow_to_lowercase(), Cow::Borrowed("abcd123")); /// assert_matches!("ὀδυσσεύς".cow_to_lowercase(), Cow::Borrowed("ὀδυσσεύς")); /// assert_matches!("ὈΔΥΣΣΕΎΣ".cow_to_lowercase(), Cow::Owned(s) if s == "ὀδυσσεύς"); /// assert_matches!("AbCd".cow_to_lowercase(), Cow::Owned(s) if s == "abcd"); /// ``` fn cow_to_lowercase(self) -> Self::Output { // `str::to_lowercase` has a tricky edgecase with handling of Σ. // We could optimise this by duplicating some code from stdlib, // but it wouldn't be particularly clean, so for now just check // if the string contains any uppercase char and let // `str::to_lowercase` rescan it again. if self.chars().any(char::is_uppercase) { Cow::Owned(self.to_lowercase()) } else { Cow::Borrowed(self) } } /// This is similar to [`str::to_ascii_uppercase`](https://doc.rust-lang.org/std/primitive.str.html#method.to_ascii_uppercase), but returns /// original slice when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("ABCD123".cow_to_ascii_uppercase(), Cow::Borrowed("ABCD123")); /// assert_matches!("ὈΔΥΣΣΕΎΣ".cow_to_ascii_uppercase(), Cow::Borrowed("ὈΔΥΣΣΕΎΣ")); /// assert_matches!("ὀδυσσεύς".cow_to_ascii_uppercase(), Cow::Borrowed("ὀδυσσεύς")); /// assert_matches!("AbCd".cow_to_ascii_uppercase(), Cow::Owned(s) if s == "ABCD"); /// ``` fn cow_to_ascii_uppercase(self) -> Self::Output { match self.as_bytes().iter().position(u8::is_ascii_lowercase) { Some(pos) => { let mut output = self.to_owned(); // We already know position of the first lowercase char, // so no need to rescan the part before it. unsafe { output.get_unchecked_mut(pos..) }.make_ascii_uppercase(); Cow::Owned(output) } None => Cow::Borrowed(self), } } /// This is similar to [`str::to_uppercase`](https://doc.rust-lang.org/std/primitive.str.html#method.to_uppercase), but returns /// original slice when possible: /// ``` /// # use cow_utils::CowUtils; /// # use assert_matches::assert_matches; /// # use std::borrow::Cow; /// assert_matches!("ABCD123".cow_to_uppercase(), Cow::Borrowed("ABCD123")); /// assert_matches!("ὈΔΥΣΣΕΎΣ".cow_to_uppercase(), Cow::Borrowed("ὈΔΥΣΣΕΎΣ")); /// assert_matches!("ὀδυσσεύς".cow_to_uppercase(), Cow::Owned(s) if s == "ὈΔΥΣΣΕΎΣ"); /// assert_matches!("AbCd".cow_to_uppercase(), Cow::Owned(s) if s == "ABCD"); /// ``` fn cow_to_uppercase(self) -> Self::Output { match self.find(char::is_lowercase) { Some(pos) => { let mut output = String::with_capacity(self.len()); // We already know position of the first lowercase char, // so no need to rescan the part before it - just copy it. output.push_str(unsafe { self.get_unchecked(..pos) }); output.extend( unsafe { self.get_unchecked(pos..) } .chars() .flat_map(char::to_uppercase), ); Cow::Owned(output) } None => Cow::Borrowed(self), } } }