src/liballoc/str.rs - third_party/rust - Git at Google

 //! Unicode string slices.
 //!
 //! *[See also the `str` primitive type](../../std/primitive.str.html).*
 //!
 //! The `&str` type is one of the two main string types, the other being `String`.
 //! Unlike its `String` counterpart, its contents are borrowed.
 //!
 //! # Basic Usage
 //!
 //! A basic string declaration of `&str` type:
 //!
 //! ```
 //! let hello_world = "Hello, World!";
 //! ```
 //!
 //! Here we have declared a string literal, also known as a string slice.
 //! String literals have a static lifetime, which means the string `hello_world`
 //! is guaranteed to be valid for the duration of the entire program.
 //! We can explicitly specify `hello_world`'s lifetime as well:
 //!
 //! ```
 //! let hello_world: &'static str = "Hello, world!";
 //! ```

 #![stable(feature = "rust1", since = "1.0.0")]
 // Many of the usings in this module are only used in the test configuration.
 // It's cleaner to just turn off the unused_imports warning than to fix them.
 #![allow(unused_imports)]

 use core::borrow::{Borrow, BorrowMut};
 use core::iter::FusedIterator;
 use core::mem;
 use core::ptr;
 use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
 use core::unicode::conversions;

 use crate::borrow::ToOwned;
 use crate::boxed::Box;
 use crate::slice::{Concat, Join, SliceIndex};
 use crate::string::String;
 use crate::vec::Vec;

 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::pattern;
 #[stable(feature = "encode_utf16", since = "1.8.0")]
 pub use core::str::EncodeUtf16;
 #[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
 pub use core::str::SplitAsciiWhitespace;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::SplitWhitespace;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
 #[stable(feature = "str_escape", since = "1.34.0")]
 pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{FromStr, Utf8Error};
 #[allow(deprecated)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{Lines, LinesAny};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{MatchIndices, RMatchIndices};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{Matches, RMatches};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplit, Split};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplitN, SplitN};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplitTerminator, SplitTerminator};

 /// Note: `str` in `Concat<str>` is not meaningful here.
 /// This type parameter of the trait only exists to enable another impl.
 #[unstable(feature = "slice_concat_ext", issue = "27747")]
 impl<S: Borrow<str>> Concat<str> for [S] {
     type Output = String;

     fn concat(slice: &Self) -> String {
         Join::join(slice, "")
     }
 }

 #[unstable(feature = "slice_concat_ext", issue = "27747")]
 impl<S: Borrow<str>> Join<&str> for [S] {
     type Output = String;

     fn join(slice: &Self, sep: &str) -> String {
         unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
     }
 }

 macro_rules! spezialize_for_lengths {
     ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {
         let mut target = $target;
         let iter = $iter;
         let sep_bytes = $separator;
         match $separator.len() {
             $(
                 // loops with hardcoded sizes run much faster
                 // specialize the cases with small separator lengths
                 $num => {
                     for s in iter {
                         copy_slice_and_advance!(target, sep_bytes);
                         copy_slice_and_advance!(target, s.borrow().as_ref());
                     }
                 },
             )*
             _ => {
                 // arbitrary non-zero size fallback
                 for s in iter {
                     copy_slice_and_advance!(target, sep_bytes);
                     copy_slice_and_advance!(target, s.borrow().as_ref());
                 }
             }
         }
     };
 }

 macro_rules! copy_slice_and_advance {
     ($target:expr, $bytes:expr) => {
         let len = $bytes.len();
         let (head, tail) = { $target }.split_at_mut(len);
         head.copy_from_slice($bytes);
         $target = tail;
     };
 }

 // Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
 // Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
 // For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
 // only user of this function. It is left in place for the time when that is fixed.
 //
 // the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
 // [T] and str both impl AsRef<[T]> for some T
 // => s.borrow().as_ref() and we always have slices
 fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
 where
     T: Copy,
     B: AsRef<[T]> + ?Sized,
     S: Borrow<B>,
 {
     let sep_len = sep.len();
     let mut iter = slice.iter();

     // the first slice is the only one without a separator preceding it
     let first = match iter.next() {
         Some(first) => first,
         None => return vec![],
     };

     // compute the exact total length of the joined Vec
     // if the `len` calculation overflows, we'll panic
     // we would have run out of memory anyway and the rest of the function requires
     // the entire Vec pre-allocated for safety
     let len = sep_len
         .checked_mul(iter.len())
         .and_then(|n| {
             slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
         })
         .expect("attempt to join into collection with len > usize::MAX");

     // crucial for safety
     let mut result = Vec::with_capacity(len);
     assert!(result.capacity() >= len);

     result.extend_from_slice(first.borrow().as_ref());

     unsafe {
         {
             let pos = result.len();
             let target = result.get_unchecked_mut(pos..len);

             // copy separator and slices over without bounds checks
             // generate loops with hardcoded offsets for small separators
             // massive improvements possible (~ x2)
             spezialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
         }
         result.set_len(len);
     }
     result
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Borrow<str> for String {
     #[inline]
     fn borrow(&self) -> &str {
         &self[..]
     }
 }

 #[stable(feature = "string_borrow_mut", since = "1.36.0")]
 impl BorrowMut<str> for String {
     #[inline]
     fn borrow_mut(&mut self) -> &mut str {
         &mut self[..]
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl ToOwned for str {
     type Owned = String;
     #[inline]
     fn to_owned(&self) -> String {
         unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
     }

     fn clone_into(&self, target: &mut String) {
         let mut b = mem::take(target).into_bytes();
         self.as_bytes().clone_into(&mut b);
         *target = unsafe { String::from_utf8_unchecked(b) }
     }
 }

 /// Methods for string slices.
 #[lang = "str_alloc"]
 #[cfg(not(test))]
 impl str {
     /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = "this is a string";
     /// let boxed_str = s.to_owned().into_boxed_str();
     /// let boxed_bytes = boxed_str.into_boxed_bytes();
     /// assert_eq!(*boxed_bytes, *s.as_bytes());
     /// ```
     #[stable(feature = "str_box_extras", since = "1.20.0")]
     #[inline]
     pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
         self.into()
     }

     /// Replaces all matches of a pattern with another string.
     ///
     /// `replace` creates a new [`String`], and copies the data from this string slice into it.
     /// While doing so, it attempts to find matches of a pattern. If it finds any, it
     /// replaces them with the replacement string slice.
     ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = "this is old";
     ///
     /// assert_eq!("this is new", s.replace("old", "new"));
     /// ```
     ///
     /// When the pattern doesn't match:
     ///
     /// ```
     /// let s = "this is old";
     /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
     /// ```
     #[must_use = "this returns the replaced string as a new allocation, \
                   without modifying the original"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
         let mut result = String::new();
         let mut last_end = 0;
         for (start, part) in self.match_indices(from) {
             result.push_str(unsafe { self.get_unchecked(last_end..start) });
             result.push_str(to);
             last_end = start + part.len();
         }
         result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
         result
     }

     /// Replaces first N matches of a pattern with another string.
     ///
     /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
     /// While doing so, it attempts to find matches of a pattern. If it finds any, it
     /// replaces them with the replacement string slice at most `count` times.
     ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = "foo foo 123 foo";
     /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
     /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
     /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
     /// ```
     ///
     /// When the pattern doesn't match:
     ///
     /// ```
     /// let s = "this is old";
     /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
     /// ```
     #[must_use = "this returns the replaced string as a new allocation, \
                   without modifying the original"]
     #[stable(feature = "str_replacen", since = "1.16.0")]
     pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
         // Hope to reduce the times of re-allocation
         let mut result = String::with_capacity(32);
         let mut last_end = 0;
         for (start, part) in self.match_indices(pat).take(count) {
             result.push_str(unsafe { self.get_unchecked(last_end..start) });
             result.push_str(to);
             last_end = start + part.len();
         }
         result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
         result
     }

     /// Returns the lowercase equivalent of this string slice, as a new [`String`].
     ///
     /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
     /// `Lowercase`.
     ///
     /// Since some characters can expand into multiple characters when changing
     /// the case, this function returns a [`String`] instead of modifying the
     /// parameter in-place.
     ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = "HELLO";
     ///
     /// assert_eq!("hello", s.to_lowercase());
     /// ```
     ///
     /// A tricky example, with sigma:
     ///
     /// ```
     /// let sigma = "Σ";
     ///
     /// assert_eq!("σ", sigma.to_lowercase());
     ///
     /// // but at the end of a word, it's ς, not σ:
     /// let odysseus = "ὈΔΥΣΣΕΎΣ";
     ///
     /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
     /// ```
     ///
     /// Languages without case are not changed:
     ///
     /// ```
     /// let new_year = "农历新年";
     ///
     /// assert_eq!(new_year, new_year.to_lowercase());
     /// ```
     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
     pub fn to_lowercase(&self) -> String {
         let mut s = String::with_capacity(self.len());
         for (i, c) in self[..].char_indices() {
             if c == 'Σ' {
                 // Σ maps to σ, except at the end of a word where it maps to ς.
                 // This is the only conditional (contextual) but language-independent mapping
                 // in `SpecialCasing.txt`,
                 // so hard-code it rather than have a generic "condition" mechanism.
                 // See https://github.com/rust-lang/rust/issues/26035
                 map_uppercase_sigma(self, i, &mut s)
             } else {
                 match conversions::to_lower(c) {
                     [a, '\0', _] => s.push(a),
                     [a, b, '\0'] => {
                         s.push(a);
                         s.push(b);
                     }
                     [a, b, c] => {
                         s.push(a);
                         s.push(b);
                         s.push(c);
                     }
                 }
             }
         }
         return s;

         fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
             // See http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
             // for the definition of `Final_Sigma`.
             debug_assert!('Σ'.len_utf8() == 2);
             let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
                 && !case_ignoreable_then_cased(from[i + 2..].chars());
             to.push_str(if is_word_final { "ς" } else { "σ" });
         }

         fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
             use core::unicode::derived_property::{Case_Ignorable, Cased};
             match iter.skip_while(|&c| Case_Ignorable(c)).next() {
                 Some(c) => Cased(c),
                 None => false,
             }
         }
     }

     /// Returns the uppercase equivalent of this string slice, as a new [`String`].
     ///
     /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
     /// `Uppercase`.
     ///
     /// Since some characters can expand into multiple characters when changing
     /// the case, this function returns a [`String`] instead of modifying the
     /// parameter in-place.
     ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = "hello";
     ///
     /// assert_eq!("HELLO", s.to_uppercase());
     /// ```
     ///
     /// Scripts without case are not changed:
     ///
     /// ```
     /// let new_year = "农历新年";
     ///
     /// assert_eq!(new_year, new_year.to_uppercase());
     /// ```
     ///
     /// One character can become multiple:
     /// ```
     /// let s = "tschüß";
     ///
     /// assert_eq!("TSCHÜSS", s.to_uppercase());
     /// ```
     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
     pub fn to_uppercase(&self) -> String {
         let mut s = String::with_capacity(self.len());
         for c in self[..].chars() {
             match conversions::to_upper(c) {
                 [a, '\0', _] => s.push(a),
                 [a, b, '\0'] => {
                     s.push(a);
                     s.push(b);
                 }
                 [a, b, c] => {
                     s.push(a);
                     s.push(b);
                     s.push(c);
                 }
             }
         }
         s
     }

     /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
     ///
     /// [`String`]: string/struct.String.html
     /// [`Box<str>`]: boxed/struct.Box.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let string = String::from("birthday gift");
     /// let boxed_str = string.clone().into_boxed_str();
     ///
     /// assert_eq!(boxed_str.into_string(), string);
     /// ```
     #[stable(feature = "box_str", since = "1.4.0")]
     #[inline]
     pub fn into_string(self: Box<str>) -> String {
         let slice = Box::<[u8]>::from(self);
         unsafe { String::from_utf8_unchecked(slice.into_vec()) }
     }

     /// Creates a new [`String`] by repeating a string `n` times.
     ///
     /// # Panics
     ///
     /// This function will panic if the capacity would overflow.
     ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
     /// ```
     ///
     /// A panic upon overflow:
     ///
     /// ```should_panic
     /// // this will panic at runtime
     /// "0123456789abcdef".repeat(usize::MAX);
     /// ```
     #[stable(feature = "repeat_str", since = "1.16.0")]
     pub fn repeat(&self, n: usize) -> String {
         unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
     }

     /// Returns a copy of this string where each character is mapped to its
     /// ASCII upper case equivalent.
     ///
     /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
     /// but non-ASCII letters are unchanged.
     ///
     /// To uppercase the value in-place, use [`make_ascii_uppercase`].
     ///
     /// To uppercase ASCII characters in addition to non-ASCII characters, use
     /// [`to_uppercase`].
     ///
     /// # Examples
     ///
     /// ```
     /// let s = "Grüße, Jürgen ❤";
     ///
     /// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
     /// ```
     ///
     /// [`make_ascii_uppercase`]: #method.make_ascii_uppercase
     /// [`to_uppercase`]: #method.to_uppercase
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_uppercase(&self) -> String {
         let mut bytes = self.as_bytes().to_vec();
         bytes.make_ascii_uppercase();
         // make_ascii_uppercase() preserves the UTF-8 invariant.
         unsafe { String::from_utf8_unchecked(bytes) }
     }

     /// Returns a copy of this string where each character is mapped to its
     /// ASCII lower case equivalent.
     ///
     /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
     /// but non-ASCII letters are unchanged.
     ///
     /// To lowercase the value in-place, use [`make_ascii_lowercase`].
     ///
     /// To lowercase ASCII characters in addition to non-ASCII characters, use
     /// [`to_lowercase`].
     ///
     /// # Examples
     ///
     /// ```
     /// let s = "Grüße, Jürgen ❤";
     ///
     /// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
     /// ```
     ///
     /// [`make_ascii_lowercase`]: #method.make_ascii_lowercase
     /// [`to_lowercase`]: #method.to_lowercase
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_lowercase(&self) -> String {
         let mut bytes = self.as_bytes().to_vec();
         bytes.make_ascii_lowercase();
         // make_ascii_lowercase() preserves the UTF-8 invariant.
         unsafe { String::from_utf8_unchecked(bytes) }
     }
 }

 /// Converts a boxed slice of bytes to a boxed string slice without checking
 /// that the string contains valid UTF-8.
 ///
 /// # Examples
 ///
 /// Basic usage:
 ///
 /// ```
 /// let smile_utf8 = Box::new([226, 152, 186]);
 /// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
 ///
 /// assert_eq!("☺", &*smile);
 /// ```
 #[stable(feature = "str_box_extras", since = "1.20.0")]
 #[inline]
 pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
     unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
 }
	//! Unicode string slices.
	//!
	//! [See also the `str` primitive type](../../std/primitive.str.html).
	//!
	//! The `&str` type is one of the two main string types, the other being `String`.
	//! Unlike its `String` counterpart, its contents are borrowed.
	//!
	//! # Basic Usage
	//!
	//! A basic string declaration of `&str` type:
	//!
	//! ```
	//! let hello_world = "Hello, World!";
	//! ```
	//!
	//! Here we have declared a string literal, also known as a string slice.
	//! String literals have a static lifetime, which means the string `hello_world`
	//! is guaranteed to be valid for the duration of the entire program.
	//! We can explicitly specify `hello_world`'s lifetime as well:
	//!
	//! ```
	//! let hello_world: &'static str = "Hello, world!";
	//! ```

	#![stable(feature = "rust1", since = "1.0.0")]
	// Many of the usings in this module are only used in the test configuration.
	// It's cleaner to just turn off the unused_imports warning than to fix them.
	#![allow(unused_imports)]

	use core::borrow::{Borrow, BorrowMut};
	use core::iter::FusedIterator;
	use core::mem;
	use core::ptr;
	use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
	use core::unicode::conversions;

	use crate::borrow::ToOwned;
	use crate::boxed::Box;
	use crate::slice::{Concat, Join, SliceIndex};
	use crate::string::String;
	use crate::vec::Vec;

	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::pattern;
	#[stable(feature = "encode_utf16", since = "1.8.0")]
	pub use core::str::EncodeUtf16;
	#[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
	pub use core::str::SplitAsciiWhitespace;
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::SplitWhitespace;
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
	#[stable(feature = "str_escape", since = "1.34.0")]
	pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{FromStr, Utf8Error};
	#[allow(deprecated)]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{Lines, LinesAny};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{MatchIndices, RMatchIndices};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{Matches, RMatches};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{RSplit, Split};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{RSplitN, SplitN};
	#[stable(feature = "rust1", since = "1.0.0")]
	pub use core::str::{RSplitTerminator, SplitTerminator};

	/// Note: `str` in `Concat<str>` is not meaningful here.
	/// This type parameter of the trait only exists to enable another impl.
	#[unstable(feature = "slice_concat_ext", issue = "27747")]
	impl<S: Borrow<str>> Concat<str> for [S] {
	type Output = String;

	fn concat(slice: &Self) -> String {
	Join::join(slice, "")
	}
	}

	#[unstable(feature = "slice_concat_ext", issue = "27747")]
	impl<S: Borrow<str>> Join<&str> for [S] {
	type Output = String;

	fn join(slice: &Self, sep: &str) -> String {
	unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
	}
	}

	macro_rules! spezialize_for_lengths {
	($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {
	let mut target = $target;
	let iter = $iter;
	let sep_bytes = $separator;
	match $separator.len() {
	$(
	// loops with hardcoded sizes run much faster
	// specialize the cases with small separator lengths
	$num => {
	for s in iter {
	copy_slice_and_advance!(target, sep_bytes);
	copy_slice_and_advance!(target, s.borrow().as_ref());
	}
	},
	)*
	_ => {
	// arbitrary non-zero size fallback
	for s in iter {
	copy_slice_and_advance!(target, sep_bytes);
	copy_slice_and_advance!(target, s.borrow().as_ref());
	}
	}
	}
	};
	}

	macro_rules! copy_slice_and_advance {
	($target:expr, $bytes:expr) => {
	let len = $bytes.len();
	let (head, tail) = { $target }.split_at_mut(len);
	head.copy_from_slice($bytes);
	$target = tail;
	};
	}

	// Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
	// Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
	// For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
	// only user of this function. It is left in place for the time when that is fixed.
	//
	// the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
	// [T] and str both impl AsRef<[T]> for some T
	// => s.borrow().as_ref() and we always have slices
	fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
	where
	T: Copy,
	B: AsRef<[T]> + ?Sized,
	S: Borrow<B>,
	{
	let sep_len = sep.len();
	let mut iter = slice.iter();

	// the first slice is the only one without a separator preceding it
	let first = match iter.next() {
	Some(first) => first,
	None => return vec![],
	};

	// compute the exact total length of the joined Vec
	// if the `len` calculation overflows, we'll panic
	// we would have run out of memory anyway and the rest of the function requires
	// the entire Vec pre-allocated for safety
	let len = sep_len
	.checked_mul(iter.len())
	.and_then(\|n\| {
	slice.iter().map(\|s\| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
	})
	.expect("attempt to join into collection with len > usize::MAX");

	// crucial for safety
	let mut result = Vec::with_capacity(len);
	assert!(result.capacity() >= len);

	result.extend_from_slice(first.borrow().as_ref());

	unsafe {
	{
	let pos = result.len();
	let target = result.get_unchecked_mut(pos..len);

	// copy separator and slices over without bounds checks
	// generate loops with hardcoded offsets for small separators
	// massive improvements possible (~ x2)
	spezialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
	}
	result.set_len(len);
	}
	result
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl Borrow<str> for String {
	#[inline]
	fn borrow(&self) -> &str {
	&self[..]
	}
	}

	#[stable(feature = "string_borrow_mut", since = "1.36.0")]
	impl BorrowMut<str> for String {
	#[inline]
	fn borrow_mut(&mut self) -> &mut str {
	&mut self[..]
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl ToOwned for str {
	type Owned = String;
	#[inline]
	fn to_owned(&self) -> String {
	unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
	}

	fn clone_into(&self, target: &mut String) {
	let mut b = mem::take(target).into_bytes();
	self.as_bytes().clone_into(&mut b);
	*target = unsafe { String::from_utf8_unchecked(b) }
	}
	}

	/// Methods for string slices.
	#[lang = "str_alloc"]
	#[cfg(not(test))]
	impl str {
	/// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let s = "this is a string";
	/// let boxed_str = s.to_owned().into_boxed_str();
	/// let boxed_bytes = boxed_str.into_boxed_bytes();
	/// assert_eq!(boxed_bytes, s.as_bytes());
	/// ```
	#[stable(feature = "str_box_extras", since = "1.20.0")]
	#[inline]
	pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
	self.into()
	}

	/// Replaces all matches of a pattern with another string.
	///
	/// `replace` creates a new [`String`], and copies the data from this string slice into it.
	/// While doing so, it attempts to find matches of a pattern. If it finds any, it
	/// replaces them with the replacement string slice.
	///
	/// [`String`]: string/struct.String.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let s = "this is old";
	///
	/// assert_eq!("this is new", s.replace("old", "new"));
	/// ```
	///
	/// When the pattern doesn't match:
	///
	/// ```
	/// let s = "this is old";
	/// assert_eq!(s, s.replace("cookie monster", "little lamb"));
	/// ```
	#[must_use = "this returns the replaced string as a new allocation, \
	without modifying the original"]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[inline]
	pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
	let mut result = String::new();
	let mut last_end = 0;
	for (start, part) in self.match_indices(from) {
	result.push_str(unsafe { self.get_unchecked(last_end..start) });
	result.push_str(to);
	last_end = start + part.len();
	}
	result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
	result
	}

	/// Replaces first N matches of a pattern with another string.
	///
	/// `replacen` creates a new [`String`], and copies the data from this string slice into it.
	/// While doing so, it attempts to find matches of a pattern. If it finds any, it
	/// replaces them with the replacement string slice at most `count` times.
	///
	/// [`String`]: string/struct.String.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let s = "foo foo 123 foo";
	/// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
	/// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
	/// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
	/// ```
	///
	/// When the pattern doesn't match:
	///
	/// ```
	/// let s = "this is old";
	/// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
	/// ```
	#[must_use = "this returns the replaced string as a new allocation, \
	without modifying the original"]
	#[stable(feature = "str_replacen", since = "1.16.0")]
	pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
	// Hope to reduce the times of re-allocation
	let mut result = String::with_capacity(32);
	let mut last_end = 0;
	for (start, part) in self.match_indices(pat).take(count) {
	result.push_str(unsafe { self.get_unchecked(last_end..start) });
	result.push_str(to);
	last_end = start + part.len();
	}
	result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
	result
	}

	/// Returns the lowercase equivalent of this string slice, as a new [`String`].
	///
	/// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
	/// `Lowercase`.
	///
	/// Since some characters can expand into multiple characters when changing
	/// the case, this function returns a [`String`] instead of modifying the
	/// parameter in-place.
	///
	/// [`String`]: string/struct.String.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let s = "HELLO";
	///
	/// assert_eq!("hello", s.to_lowercase());
	/// ```
	///
	/// A tricky example, with sigma:
	///
	/// ```
	/// let sigma = "Σ";
	///
	/// assert_eq!("σ", sigma.to_lowercase());
	///
	/// // but at the end of a word, it's ς, not σ:
	/// let odysseus = "ὈΔΥΣΣΕΎΣ";
	///
	/// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
	/// ```
	///
	/// Languages without case are not changed:
	///
	/// ```
	/// let new_year = "农历新年";
	///
	/// assert_eq!(new_year, new_year.to_lowercase());
	/// ```
	#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
	pub fn to_lowercase(&self) -> String {
	let mut s = String::with_capacity(self.len());
	for (i, c) in self[..].char_indices() {
	if c == 'Σ' {
	// Σ maps to σ, except at the end of a word where it maps to ς.
	// This is the only conditional (contextual) but language-independent mapping
	// in `SpecialCasing.txt`,
	// so hard-code it rather than have a generic "condition" mechanism.
	// See https://github.com/rust-lang/rust/issues/26035
	map_uppercase_sigma(self, i, &mut s)
	} else {
	match conversions::to_lower(c) {
	[a, '\0', _] => s.push(a),
	[a, b, '\0'] => {
	s.push(a);
	s.push(b);
	}
	[a, b, c] => {
	s.push(a);
	s.push(b);
	s.push(c);
	}
	}
	}
	}
	return s;

	fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
	// See http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
	// for the definition of `Final_Sigma`.
	debug_assert!('Σ'.len_utf8() == 2);
	let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
	&& !case_ignoreable_then_cased(from[i + 2..].chars());
	to.push_str(if is_word_final { "ς" } else { "σ" });
	}

	fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
	use core::unicode::derived_property::{Case_Ignorable, Cased};
	match iter.skip_while(\|&c\| Case_Ignorable(c)).next() {
	Some(c) => Cased(c),
	None => false,
	}
	}
	}

	/// Returns the uppercase equivalent of this string slice, as a new [`String`].
	///
	/// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
	/// `Uppercase`.
	///
	/// Since some characters can expand into multiple characters when changing
	/// the case, this function returns a [`String`] instead of modifying the
	/// parameter in-place.
	///
	/// [`String`]: string/struct.String.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let s = "hello";
	///
	/// assert_eq!("HELLO", s.to_uppercase());
	/// ```
	///
	/// Scripts without case are not changed:
	///
	/// ```
	/// let new_year = "农历新年";
	///
	/// assert_eq!(new_year, new_year.to_uppercase());
	/// ```
	///
	/// One character can become multiple:
	/// ```
	/// let s = "tschüß";
	///
	/// assert_eq!("TSCHÜSS", s.to_uppercase());
	/// ```
	#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
	pub fn to_uppercase(&self) -> String {
	let mut s = String::with_capacity(self.len());
	for c in self[..].chars() {
	match conversions::to_upper(c) {
	[a, '\0', _] => s.push(a),
	[a, b, '\0'] => {
	s.push(a);
	s.push(b);
	}
	[a, b, c] => {
	s.push(a);
	s.push(b);
	s.push(c);
	}
	}
	}
	s
	}

	/// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
	///
	/// [`String`]: string/struct.String.html
	/// [`Box<str>`]: boxed/struct.Box.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let string = String::from("birthday gift");
	/// let boxed_str = string.clone().into_boxed_str();
	///
	/// assert_eq!(boxed_str.into_string(), string);
	/// ```
	#[stable(feature = "box_str", since = "1.4.0")]
	#[inline]
	pub fn into_string(self: Box<str>) -> String {
	let slice = Box::<[u8]>::from(self);
	unsafe { String::from_utf8_unchecked(slice.into_vec()) }
	}

	/// Creates a new [`String`] by repeating a string `n` times.
	///
	/// # Panics
	///
	/// This function will panic if the capacity would overflow.
	///
	/// [`String`]: string/struct.String.html
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
	/// ```
	///
	/// A panic upon overflow:
	///
	/// ```should_panic
	/// // this will panic at runtime
	/// "0123456789abcdef".repeat(usize::MAX);
	/// ```
	#[stable(feature = "repeat_str", since = "1.16.0")]
	pub fn repeat(&self, n: usize) -> String {
	unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
	}

	/// Returns a copy of this string where each character is mapped to its
	/// ASCII upper case equivalent.
	///
	/// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
	/// but non-ASCII letters are unchanged.
	///
	/// To uppercase the value in-place, use [`make_ascii_uppercase`].
	///
	/// To uppercase ASCII characters in addition to non-ASCII characters, use
	/// [`to_uppercase`].
	///
	/// # Examples
	///
	/// ```
	/// let s = "Grüße, Jürgen ❤";
	///
	/// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
	/// ```
	///
	/// [`make_ascii_uppercase`]: #method.make_ascii_uppercase
	/// [`to_uppercase`]: #method.to_uppercase
	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
	#[inline]
	pub fn to_ascii_uppercase(&self) -> String {
	let mut bytes = self.as_bytes().to_vec();
	bytes.make_ascii_uppercase();
	// make_ascii_uppercase() preserves the UTF-8 invariant.
	unsafe { String::from_utf8_unchecked(bytes) }
	}

	/// Returns a copy of this string where each character is mapped to its
	/// ASCII lower case equivalent.
	///
	/// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
	/// but non-ASCII letters are unchanged.
	///
	/// To lowercase the value in-place, use [`make_ascii_lowercase`].
	///
	/// To lowercase ASCII characters in addition to non-ASCII characters, use
	/// [`to_lowercase`].
	///
	/// # Examples
	///
	/// ```
	/// let s = "Grüße, Jürgen ❤";
	///
	/// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
	/// ```
	///
	/// [`make_ascii_lowercase`]: #method.make_ascii_lowercase
	/// [`to_lowercase`]: #method.to_lowercase
	#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
	#[inline]
	pub fn to_ascii_lowercase(&self) -> String {
	let mut bytes = self.as_bytes().to_vec();
	bytes.make_ascii_lowercase();
	// make_ascii_lowercase() preserves the UTF-8 invariant.
	unsafe { String::from_utf8_unchecked(bytes) }
	}
	}

	/// Converts a boxed slice of bytes to a boxed string slice without checking
	/// that the string contains valid UTF-8.
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// let smile_utf8 = Box::new([226, 152, 186]);
	/// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
	///
	/// assert_eq!("☺", &*smile);
	/// ```
	#[stable(feature = "str_box_extras", since = "1.20.0")]
	#[inline]
	pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
	unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
	}