traits.rs - source
Description: Source of the Rust file `library/core/src/str/traits.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Trait implementations for `str`.

    use crate::cmp::Ordering;
    use crate::ops;
    use crate::ptr;
    use crate::slice::SliceIndex;

    use super::ParseBoolError;

    /// Implements ordering of strings.
    ///
    /// Strings are ordered  [lexicographically](Ord#lexicographical-comparison) by their byte values. This orders Unicode code
    /// points based on their positions in the code charts. This is not necessarily the same as
    /// "alphabetical" order, which varies by language and locale. Sorting strings according to
    /// culturally-accepted standards requires locale-specific data that is outside the scope of
    /// the `str` type.
    #[stable(feature = "rust1", since = "1.0.0")]
    impl Ord for str {
        #[inline]
        fn cmp(&self, other: &str) -> Ordering {
            self.as_bytes().cmp(other.as_bytes())
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl PartialEq for str {
        #[inline]
        fn eq(&self, other: &str) -> bool {
            self.as_bytes() == other.as_bytes()
        }
        #[inline]
        fn ne(&self, other: &str) -> bool {
            !(*self).eq(other)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Eq for str {}

    /// Implements comparison operations on strings.
    ///
    /// Strings are compared [lexicographically](Ord#lexicographical-comparison) by their byte values. This compares Unicode code
    /// points based on their positions in the code charts. This is not necessarily the same as
    /// "alphabetical" order, which varies by language and locale. Comparing strings according to
    /// culturally-accepted standards requires locale-specific data that is outside the scope of
    /// the `str` type.
    #[stable(feature = "rust1", since = "1.0.0")]
    impl PartialOrd for str {
        #[inline]
        fn partial_cmp(&self, other: &str) -> Option<Ordering> {
            Some(self.cmp(other))
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<I> ops::Index<I> for str
    where
        I: SliceIndex<str>,
    {
        type Output = I::Output;

        #[inline]
        fn index(&self, index: I) -> &I::Output {
            index.index(self)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<I> ops::IndexMut<I> for str
    where
        I: SliceIndex<str>,
    {
        #[inline]
        fn index_mut(&mut self, index: I) -> &mut I::Output {
            index.index_mut(self)
        }
    }

    #[inline(never)]
    #[cold]
    #[track_caller]
    fn str_index_overflow_fail() -> ! {
        panic!("attempted to index str up to maximum usize");
    }

    /// Implements substring slicing with syntax `&self[..]` or `&mut self[..]`.
    ///
    /// Returns a slice of the whole string, i.e., returns `&self` or `&mut
    /// self`. Equivalent to `&self[0 .. len]` or `&mut self[0 .. len]`. Unlike
    /// other indexing operations, this can never panic.
    ///
    /// This operation is *O*(1).
    ///
    /// Prior to 1.20.0, these indexing operations were still supported by
    /// direct implementation of `Index` and `IndexMut`.
    ///
    /// Equivalent to `&self[0 .. len]` or `&mut self[0 .. len]`.
    #[stable(feature = "str_checked_slicing", since = "1.20.0")]
    unsafe impl SliceIndex<str> for ops::RangeFull {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            Some(slice)
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            Some(slice)
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            slice
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            slice
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            slice
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            slice
        }
    }

    /// Implements substring slicing with syntax `&self[begin .. end]` or `&mut
    /// self[begin .. end]`.
    ///
    /// Returns a slice of the given string from the byte range
    /// [`begin`, `end`).
    ///
    /// This operation is *O*(1).
    ///
    /// Prior to 1.20.0, these indexing operations were still supported by
    /// direct implementation of `Index` and `IndexMut`.
    ///
    /// # Panics
    ///
    /// Panics if `begin` or `end` does not point to the starting byte offset of
    /// a character (as defined by `is_char_boundary`), if `begin > end`, or if
    /// `end > len`.
    ///
    /// # Examples
    ///
    /// ```
    /// let s = "Löwe 老虎 Léopard";
    /// assert_eq!(&s[0 .. 1], "L");
    ///
    /// assert_eq!(&s[1 .. 9], "öwe 老");
    ///
    /// // these will panic:
    /// // byte 2 lies within `ö`:
    /// // &s[2 ..3];
    ///
    /// // byte 8 lies within `老`
    /// // &s[1 .. 8];
    ///
    /// // byte 100 is outside the string
    /// // &s[3 .. 100];
    /// ```
    #[stable(feature = "str_checked_slicing", since = "1.20.0")]
    unsafe impl SliceIndex<str> for ops::Range<usize> {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            if self.start <= self.end
                && slice.is_char_boundary(self.start)
                && slice.is_char_boundary(self.end)
            {
                // SAFETY: just checked that `start` and `end` are on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                // We also checked char boundaries, so this is valid UTF-8.
                Some(unsafe { &*self.get_unchecked(slice) })
            } else {
                None
            }
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            if self.start <= self.end
                && slice.is_char_boundary(self.start)
                && slice.is_char_boundary(self.end)
            {
                // SAFETY: just checked that `start` and `end` are on a char boundary.
                // We know the pointer is unique because we got it from `slice`.
                Some(unsafe { &mut *self.get_unchecked_mut(slice) })
            } else {
                None
            }
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            let slice = slice as *const [u8];
            // SAFETY: the caller guarantees that `self` is in bounds of `slice`
            // which satisfies all the conditions for `add`.
            let ptr = unsafe { slice.as_ptr().add(self.start) };
            let len = self.end - self.start;
            ptr::slice_from_raw_parts(ptr, len) as *const str
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            let slice = slice as *mut [u8];
            // SAFETY: see comments for `get_unchecked`.
            let ptr = unsafe { slice.as_mut_ptr().add(self.start) };
            let len = self.end - self.start;
            ptr::slice_from_raw_parts_mut(ptr, len) as *mut str
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            let (start, end) = (self.start, self.end);
            match self.get(slice) {
                Some(s) => s,
                None => super::slice_error_fail(slice, start, end),
            }
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            // is_char_boundary checks that the index is in [0, .len()]
            // cannot reuse `get` as above, because of NLL trouble
            if self.start <= self.end
                && slice.is_char_boundary(self.start)
                && slice.is_char_boundary(self.end)
            {
                // SAFETY: just checked that `start` and `end` are on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                unsafe { &mut *self.get_unchecked_mut(slice) }
            } else {
                super::slice_error_fail(slice, self.start, self.end)
            }
        }
    }

    /// Implements substring slicing with syntax `&self[.. end]` or `&mut
    /// self[.. end]`.
    ///
    /// Returns a slice of the given string from the byte range [`0`, `end`).
    /// Equivalent to `&self[0 .. end]` or `&mut self[0 .. end]`.
    ///
    /// This operation is *O*(1).
    ///
    /// Prior to 1.20.0, these indexing operations were still supported by
    /// direct implementation of `Index` and `IndexMut`.
    ///
    /// # Panics
    ///
    /// Panics if `end` does not point to the starting byte offset of a
    /// character (as defined by `is_char_boundary`), or if `end > len`.
    #[stable(feature = "str_checked_slicing", since = "1.20.0")]
    unsafe impl SliceIndex<str> for ops::RangeTo<usize> {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            if slice.is_char_boundary(self.end) {
                // SAFETY: just checked that `end` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                Some(unsafe { &*self.get_unchecked(slice) })
            } else {
                None
            }
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            if slice.is_char_boundary(self.end) {
                // SAFETY: just checked that `end` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                Some(unsafe { &mut *self.get_unchecked_mut(slice) })
            } else {
                None
            }
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            let slice = slice as *const [u8];
            let ptr = slice.as_ptr();
            ptr::slice_from_raw_parts(ptr, self.end) as *const str
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            let slice = slice as *mut [u8];
            let ptr = slice.as_mut_ptr();
            ptr::slice_from_raw_parts_mut(ptr, self.end) as *mut str
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            let end = self.end;
            match self.get(slice) {
                Some(s) => s,
                None => super::slice_error_fail(slice, 0, end),
            }
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            if slice.is_char_boundary(self.end) {
                // SAFETY: just checked that `end` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                unsafe { &mut *self.get_unchecked_mut(slice) }
            } else {
                super::slice_error_fail(slice, 0, self.end)
            }
        }
    }

    /// Implements substring slicing with syntax `&self[begin ..]` or `&mut
    /// self[begin ..]`.
    ///
    /// Returns a slice of the given string from the byte range [`begin`,
    /// `len`). Equivalent to `&self[begin .. len]` or `&mut self[begin ..
    /// len]`.
    ///
    /// This operation is *O*(1).
    ///
    /// Prior to 1.20.0, these indexing operations were still supported by
    /// direct implementation of `Index` and `IndexMut`.
    ///
    /// # Panics
    ///
    /// Panics if `begin` does not point to the starting byte offset of
    /// a character (as defined by `is_char_boundary`), or if `begin > len`.
    #[stable(feature = "str_checked_slicing", since = "1.20.0")]
    unsafe impl SliceIndex<str> for ops::RangeFrom<usize> {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            if slice.is_char_boundary(self.start) {
                // SAFETY: just checked that `start` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                Some(unsafe { &*self.get_unchecked(slice) })
            } else {
                None
            }
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            if slice.is_char_boundary(self.start) {
                // SAFETY: just checked that `start` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                Some(unsafe { &mut *self.get_unchecked_mut(slice) })
            } else {
                None
            }
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            let slice = slice as *const [u8];
            // SAFETY: the caller guarantees that `self` is in bounds of `slice`
            // which satisfies all the conditions for `add`.
            let ptr = unsafe { slice.as_ptr().add(self.start) };
            let len = slice.len() - self.start;
            ptr::slice_from_raw_parts(ptr, len) as *const str
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            let slice = slice as *mut [u8];
            // SAFETY: identical to `get_unchecked`.
            let ptr = unsafe { slice.as_mut_ptr().add(self.start) };
            let len = slice.len() - self.start;
            ptr::slice_from_raw_parts_mut(ptr, len) as *mut str
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            let (start, end) = (self.start, slice.len());
            match self.get(slice) {
                Some(s) => s,
                None => super::slice_error_fail(slice, start, end),
            }
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            if slice.is_char_boundary(self.start) {
                // SAFETY: just checked that `start` is on a char boundary,
                // and we are passing in a safe reference, so the return value will also be one.
                unsafe { &mut *self.get_unchecked_mut(slice) }
            } else {
                super::slice_error_fail(slice, self.start, slice.len())
            }
        }
    }

    /// Implements substring slicing with syntax `&self[begin ..= end]` or `&mut
    /// self[begin ..= end]`.
    ///
    /// Returns a slice of the given string from the byte range
    /// [`begin`, `end`]. Equivalent to `&self [begin .. end + 1]` or `&mut
    /// self[begin .. end + 1]`, except if `end` has the maximum value for
    /// `usize`.
    ///
    /// This operation is *O*(1).
    ///
    /// # Panics
    ///
    /// Panics if `begin` does not point to the starting byte offset of
    /// a character (as defined by `is_char_boundary`), if `end` does not point
    /// to the ending byte offset of a character (`end + 1` is either a starting
    /// byte offset or equal to `len`), if `begin > end`, or if `end >= len`.
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    unsafe impl SliceIndex<str> for ops::RangeInclusive<usize> {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            if *self.end() == usize::MAX { None } else { self.into_slice_range().get(slice) }
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            if *self.end() == usize::MAX { None } else { self.into_slice_range().get_mut(slice) }
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            // SAFETY: the caller must uphold the safety contract for `get_unchecked`.
            unsafe { self.into_slice_range().get_unchecked(slice) }
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            // SAFETY: the caller must uphold the safety contract for `get_unchecked_mut`.
            unsafe { self.into_slice_range().get_unchecked_mut(slice) }
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            if *self.end() == usize::MAX {
                str_index_overflow_fail();
            }
            self.into_slice_range().index(slice)
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            if *self.end() == usize::MAX {
                str_index_overflow_fail();
            }
            self.into_slice_range().index_mut(slice)
        }
    }

    /// Implements substring slicing with syntax `&self[..= end]` or `&mut
    /// self[..= end]`.
    ///
    /// Returns a slice of the given string from the byte range [0, `end`].
    /// Equivalent to `&self [0 .. end + 1]`, except if `end` has the maximum
    /// value for `usize`.
    ///
    /// This operation is *O*(1).
    ///
    /// # Panics
    ///
    /// Panics if `end` does not point to the ending byte offset of a character
    /// (`end + 1` is either a starting byte offset as defined by
    /// `is_char_boundary`, or equal to `len`), or if `end >= len`.
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    unsafe impl SliceIndex<str> for ops::RangeToInclusive<usize> {
        type Output = str;
        #[inline]
        fn get(self, slice: &str) -> Option<&Self::Output> {
            if self.end == usize::MAX { None } else { (..self.end + 1).get(slice) }
        }
        #[inline]
        fn get_mut(self, slice: &mut str) -> Option<&mut Self::Output> {
            if self.end == usize::MAX { None } else { (..self.end + 1).get_mut(slice) }
        }
        #[inline]
        unsafe fn get_unchecked(self, slice: *const str) -> *const Self::Output {
            // SAFETY: the caller must uphold the safety contract for `get_unchecked`.
            unsafe { (..self.end + 1).get_unchecked(slice) }
        }
        #[inline]
        unsafe fn get_unchecked_mut(self, slice: *mut str) -> *mut Self::Output {
            // SAFETY: the caller must uphold the safety contract for `get_unchecked_mut`.
            unsafe { (..self.end + 1).get_unchecked_mut(slice) }
        }
        #[inline]
        fn index(self, slice: &str) -> &Self::Output {
            if self.end == usize::MAX {
                str_index_overflow_fail();
            }
            (..self.end + 1).index(slice)
        }
        #[inline]
        fn index_mut(self, slice: &mut str) -> &mut Self::Output {
            if self.end == usize::MAX {
                str_index_overflow_fail();
            }
            (..self.end + 1).index_mut(slice)
        }
    }

    /// Parse a value from a string
    ///
    /// `FromStr`'s [`from_str`] method is often used implicitly, through
    /// [`str`]'s [`parse`] method. See [`parse`]'s documentation for examples.
    ///
    /// [`from_str`]: FromStr::from_str
    /// [`parse`]: str::parse
    ///
    /// `FromStr` does not have a lifetime parameter, and so you can only parse types
    /// that do not contain a lifetime parameter themselves. In other words, you can
    /// parse an `i32` with `FromStr`, but not a `&i32`. You can parse a struct that
    /// contains an `i32`, but not one that contains an `&i32`.
    ///
    /// # Examples
    ///
    /// Basic implementation of `FromStr` on an example `Point` type:
    ///
    /// ```
    /// use std::str::FromStr;
    /// use std::num::ParseIntError;
    ///
    /// #[derive(Debug, PartialEq)]
    /// struct Point {
    ///     x: i32,
    ///     y: i32
    /// }
    ///
    /// impl FromStr for Point {
    ///     type Err = ParseIntError;
    ///
    ///     fn from_str(s: &str) -> Result<Self, Self::Err> {
    ///         let coords: Vec<&str> = s.trim_matches(|p| p == '(' || p == ')' )
    ///                                  .split(',')
    ///                                  .collect();
    ///
    ///         let x_fromstr = coords[0].parse::<i32>()?;
    ///         let y_fromstr = coords[1].parse::<i32>()?;
    ///
    ///         Ok(Point { x: x_fromstr, y: y_fromstr })
    ///     }
    /// }
    ///
    /// let p = Point::from_str("(1,2)");
    /// assert_eq!(p.unwrap(), Point{ x: 1, y: 2} )
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait FromStr: Sized {
        /// The associated error which can be returned from parsing.
        #[stable(feature = "rust1", since = "1.0.0")]
        type Err;

        /// Parses a string `s` to return a value of this type.
        ///
        /// If parsing succeeds, return the value inside [`Ok`], otherwise
        /// when the string is ill-formatted return an error specific to the
        /// inside [`Err`]. The error type is specific to implementation of the trait.
        ///
        /// # Examples
        ///
        /// Basic usage with [`i32`][ithirtytwo], a type that implements `FromStr`:
        ///
        /// [ithirtytwo]: ../../std/primitive.i32.html
        ///
        /// ```
        /// use std::str::FromStr;
        ///
        /// let s = "5";
        /// let x = i32::from_str(s).unwrap();
        ///
        /// assert_eq!(5, x);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn from_str(s: &str) -> Result<Self, Self::Err>;
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl FromStr for bool {
        type Err = ParseBoolError;

        /// Parse a `bool` from a string.
        ///
        /// Yields a `Result<bool, ParseBoolError>`, because `s` may or may not
        /// actually be parseable.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::str::FromStr;
        ///
        /// assert_eq!(FromStr::from_str("true"), Ok(true));
        /// assert_eq!(FromStr::from_str("false"), Ok(false));
        /// assert!(<bool as FromStr>::from_str("not even a boolean").is_err());
        /// ```
        ///
        /// Note, in many cases, the `.parse()` method on `str` is more proper.
        ///
        /// ```
        /// assert_eq!("true".parse(), Ok(true));
        /// assert_eq!("false".parse(), Ok(false));
        /// assert!("not even a boolean".parse::<bool>().is_err());
        /// ```
        #[inline]
        fn from_str(s: &str) -> Result<bool, ParseBoolError> {
            match s {
                "true" => Ok(true),
                "false" => Ok(false),
                _ => Err(ParseBoolError { _priv: () }),
            }
        }
    }