tinystr/

ascii.rs

// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::asciibyte::AsciiByte;
use crate::int_ops::{Aligned4, Aligned8};
use crate::ParseError;
#[cfg(feature = "alloc")]
use alloc::string::String;
use core::borrow::Borrow;
use core::fmt;
use core::ops::Deref;
use core::str::{self, FromStr};

#[repr(transparent)]
#[derive(PartialEq, Eq, Ord, PartialOrd, Copy, Clone, Hash)]
pub struct TinyAsciiStr<const N: usize> {
    bytes: [AsciiByte; N],
}

impl<const N: usize> TinyAsciiStr<N> {
    /// The empty string.
    pub const EMPTY: Self = Self {
        bytes: [AsciiByte::B0; N],
    };

    #[inline]
    pub const fn try_from_str(s: &str) -> Result<Self, ParseError> {
        Self::try_from_utf8(s.as_bytes())
    }

    /// Creates a `TinyAsciiStr<N>` from the given UTF-8 slice.
    /// `code_units` may contain at most `N` non-null ASCII code points.
    #[inline]
    pub const fn try_from_utf8(code_units: &[u8]) -> Result<Self, ParseError> {
        Self::try_from_utf8_inner(code_units, false)
    }

    /// Creates a `TinyAsciiStr<N>` from the given UTF-16 slice.
    /// `code_units` may contain at most `N` non-null ASCII code points.
    #[inline]
    pub const fn try_from_utf16(code_units: &[u16]) -> Result<Self, ParseError> {
        Self::try_from_utf16_inner(code_units, 0, code_units.len(), false)
    }

    /// Creates a `TinyAsciiStr<N>` from a UTF-8 slice, replacing invalid code units.
    ///
    /// Invalid code units, as well as null or non-ASCII code points
    /// (i.e. those outside the range `U+0001..=U+007F`)
    /// will be replaced with the replacement byte.
    ///
    /// The input slice will be truncated if its length exceeds `N`.
    ///
    /// # Panics
    ///
    /// Panics if `replacement` is not a non-null ASCII byte (i.e. not in `1..=127`).
    pub const fn from_utf8_lossy(code_units: &[u8], replacement: u8) -> Self {
        assert!(
            replacement > 0 && replacement < 0x80,
            "replacement must be a non-null ASCII byte (1..=127)"
        );
        let mut out = [0; N];
        let mut i = 0;
        // Ord is not available in const, so no `.min(N)`
        let len = if code_units.len() > N {
            N
        } else {
            code_units.len()
        };

        // Indexing is protected by the len check above
        #[expect(clippy::indexing_slicing)]
        while i < len {
            let b = code_units[i];
            if b > 0 && b < 0x80 {
                out[i] = b;
            } else {
                out[i] = replacement;
            }
            i += 1;
        }

        Self {
            // SAFETY: `out` only contains ASCII bytes and has same size as `self.bytes`
            bytes: unsafe { AsciiByte::to_ascii_byte_array(&out) },
        }
    }

    /// Creates a `TinyAsciiStr<N>` from a UTF-16 slice, replacing invalid code units.
    ///
    /// Invalid code units, as well as null or non-ASCII code points
    /// (i.e. those outside the range `U+0001..=U+007F`)
    /// will be replaced with the replacement byte.
    ///
    /// The input slice will be truncated if its length exceeds `N`.
    ///
    /// # Panics
    ///
    /// Panics if `replacement` is not a non-null ASCII byte (i.e. not in `1..=127`).
    pub const fn from_utf16_lossy(code_units: &[u16], replacement: u8) -> Self {
        assert!(
            replacement > 0 && replacement < 0x80,
            "replacement must be a non-null ASCII byte (1..=127)"
        );
        let mut out = [0; N];
        let mut i = 0;
        // Ord is not available in const, so no `.min(N)`
        let len = if code_units.len() > N {
            N
        } else {
            code_units.len()
        };

        // Indexing is protected by the len check above
        #[expect(clippy::indexing_slicing)]
        while i < len {
            let b = code_units[i];
            if b > 0 && b < 0x80 {
                out[i] = b as u8;
            } else {
                out[i] = replacement;
            }
            i += 1;
        }

        Self {
            // SAFETY: `out` only contains ASCII bytes and has same size as `self.bytes`
            bytes: unsafe { AsciiByte::to_ascii_byte_array(&out) },
        }
    }

    /// Attempts to parse a fixed-length byte array to a `TinyAsciiStr`.
    ///
    /// The byte array may contain trailing NUL bytes.
    ///
    /// # Example
    ///
    /// ```
    /// use tinystr::tinystr;
    /// use tinystr::TinyAsciiStr;
    ///
    /// assert_eq!(
    ///     TinyAsciiStr::<3>::try_from_raw(*b"GB\0"),
    ///     Ok(tinystr!(3, "GB"))
    /// );
    /// assert_eq!(
    ///     TinyAsciiStr::<3>::try_from_raw(*b"USD"),
    ///     Ok(tinystr!(3, "USD"))
    /// );
    /// assert!(TinyAsciiStr::<3>::try_from_raw(*b"\0A\0").is_err());
    /// ```
    pub const fn try_from_raw(raw: [u8; N]) -> Result<Self, ParseError> {
        Self::try_from_utf8_inner(&raw, true)
    }

    pub(crate) const fn try_from_utf8_inner(
        code_units: &[u8],
        allow_trailing_null: bool,
    ) -> Result<Self, ParseError> {
        if code_units.len() > N {
            return Err(ParseError::TooLong {
                max: N,
                len: code_units.len(),
            });
        }

        let mut out = [0; N];
        let mut i = 0;
        let mut found_null = false;
        // Indexing is protected by TinyStrError::TooLarge
        #[expect(clippy::indexing_slicing)]
        while i < code_units.len() {
            let b = code_units[i];

            if b == 0 {
                found_null = true;
            } else if b >= 0x80 {
                return Err(ParseError::NonAscii);
            } else if found_null {
                // Error if there are contentful bytes after null
                return Err(ParseError::ContainsNull);
            }
            out[i] = b;

            i += 1;
        }

        if !allow_trailing_null && found_null {
            // We found some trailing nulls, error
            return Err(ParseError::ContainsNull);
        }

        Ok(Self {
            // SAFETY: `out` only contains ASCII bytes and has same size as `self.bytes`
            bytes: unsafe { AsciiByte::to_ascii_byte_array(&out) },
        })
    }

    pub(crate) const fn try_from_utf16_inner(
        code_units: &[u16],
        start: usize,
        end: usize,
        allow_trailing_null: bool,
    ) -> Result<Self, ParseError> {
        let len = end - start;
        if len > N {
            return Err(ParseError::TooLong { max: N, len });
        }

        let mut out = [0; N];
        let mut i = 0;
        let mut found_null = false;
        // Indexing is protected by TinyStrError::TooLarge
        #[expect(clippy::indexing_slicing)]
        while i < len {
            let b = code_units[start + i];

            if b == 0 {
                found_null = true;
            } else if b >= 0x80 {
                return Err(ParseError::NonAscii);
            } else if found_null {
                // Error if there are contentful bytes after null
                return Err(ParseError::ContainsNull);
            }
            out[i] = b as u8;

            i += 1;
        }

        if !allow_trailing_null && found_null {
            // We found some trailing nulls, error
            return Err(ParseError::ContainsNull);
        }

        Ok(Self {
            // SAFETY: `out` only contains ASCII bytes and has same size as `self.bytes`
            bytes: unsafe { AsciiByte::to_ascii_byte_array(&out) },
        })
    }

    /// Creates a `TinyAsciiStr<N>` containing the decimal representation of
    /// the given unsigned integer.
    ///
    /// If the number of decimal digits exceeds `N`, the highest-magnitude
    /// digits are truncated, and the lowest-magnitude digits are returned
    /// as the error.
    ///
    /// Note: this function takes a u32. Larger integer types should probably
    /// not be stored in a `TinyAsciiStr`.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::tinystr;
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s0_4 = TinyAsciiStr::<4>::new_unsigned_decimal(0).unwrap();
    /// let s456_4 = TinyAsciiStr::<4>::new_unsigned_decimal(456).unwrap();
    /// let s456_3 = TinyAsciiStr::<3>::new_unsigned_decimal(456).unwrap();
    /// let s456_2 = TinyAsciiStr::<2>::new_unsigned_decimal(456).unwrap_err();
    ///
    /// assert_eq!(s0_4, tinystr!(4, "0"));
    /// assert_eq!(s456_4, tinystr!(4, "456"));
    /// assert_eq!(s456_3, tinystr!(3, "456"));
    /// assert_eq!(s456_2, tinystr!(2, "56"));
    /// ```
    ///
    /// Example with saturating the value:
    ///
    /// ```
    /// use tinystr::tinystr;
    /// use tinystr::TinyAsciiStr;
    ///
    /// let str_truncated =
    ///     TinyAsciiStr::<2>::new_unsigned_decimal(456).unwrap_or_else(|s| s);
    /// let str_saturated = TinyAsciiStr::<2>::new_unsigned_decimal(456)
    ///     .unwrap_or(tinystr!(2, "99"));
    ///
    /// assert_eq!(str_truncated, tinystr!(2, "56"));
    /// assert_eq!(str_saturated, tinystr!(2, "99"));
    /// ```
    pub fn new_unsigned_decimal(number: u32) -> Result<Self, Self> {
        let mut bytes = [AsciiByte::B0; N];
        let mut x = number;
        let mut i = 0usize;
        #[expect(clippy::indexing_slicing)] // in-range: i < N
        while i < N && (x != 0 || i == 0) {
            bytes[N - i - 1] = AsciiByte::from_decimal_digit((x % 10) as u8);
            x /= 10;
            i += 1;
        }
        if i < N {
            bytes.copy_within((N - i)..N, 0);
            bytes[i..N].fill(AsciiByte::B0);
        }
        let s = Self { bytes };
        if x != 0 {
            Err(s)
        } else {
            Ok(s)
        }
    }

    #[inline]
    pub const fn as_str(&self) -> &str {
        // as_utf8 is valid utf8
        unsafe { str::from_utf8_unchecked(self.as_utf8()) }
    }

    #[inline]
    #[must_use]
    pub const fn len(&self) -> usize {
        if N <= 4 {
            Aligned4::from_ascii_bytes(&self.bytes).len()
        } else if N <= 8 {
            Aligned8::from_ascii_bytes(&self.bytes).len()
        } else {
            let mut i = 0;
            #[expect(clippy::indexing_slicing)] // < N is safe
            while i < N && self.bytes[i] as u8 != AsciiByte::B0 as u8 {
                i += 1
            }
            i
        }
    }

    #[inline]
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        self.bytes[0] as u8 == AsciiByte::B0 as u8
    }

    #[inline]
    #[must_use]
    pub const fn as_utf8(&self) -> &[u8] {
        // Safe because `self.bytes.as_slice()` pointer-casts to `&[u8]`,
        // and changing the length of that slice to self.len() < N is safe.
        unsafe {
            core::slice::from_raw_parts(self.bytes.as_slice().as_ptr() as *const u8, self.len())
        }
    }

    #[inline]
    #[must_use]
    pub const fn all_bytes(&self) -> &[u8; N] {
        // SAFETY: `self.bytes` has same size as [u8; N]
        unsafe { &*(self.bytes.as_ptr() as *const [u8; N]) }
    }

    #[inline]
    #[must_use]
    /// Resizes a `TinyAsciiStr<N>` to a `TinyAsciiStr<M>`.
    ///
    /// If `M < len()` the string gets truncated, otherwise only the
    /// memory representation changes.
    pub const fn resize<const M: usize>(self) -> TinyAsciiStr<M> {
        let mut bytes = [0; M];
        let mut i = 0;
        // Indexing is protected by the loop guard
        #[expect(clippy::indexing_slicing)]
        while i < M && i < N {
            bytes[i] = self.bytes[i] as u8;
            i += 1;
        }
        // `self.bytes` only contains ASCII bytes, with no null bytes between
        // ASCII characters, so this also holds for `bytes`.
        unsafe { TinyAsciiStr::from_utf8_unchecked(bytes) }
    }

    #[inline]
    #[must_use]
    /// Returns a `TinyAsciiStr<Q>` with the concatenation of this string,
    /// `TinyAsciiStr<N>`, and another string, `TinyAsciiStr<M>`.
    ///
    /// If `Q < N + M`, the string gets truncated.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::tinystr;
    /// use tinystr::TinyAsciiStr;
    ///
    /// let abc = tinystr!(6, "abc");
    /// let defg = tinystr!(6, "defg");
    ///
    /// // The concatenation is successful if Q is large enough...
    /// assert_eq!(abc.concat(defg), tinystr!(16, "abcdefg"));
    /// assert_eq!(abc.concat(defg), tinystr!(12, "abcdefg"));
    /// assert_eq!(abc.concat(defg), tinystr!(8, "abcdefg"));
    /// assert_eq!(abc.concat(defg), tinystr!(7, "abcdefg"));
    ///
    /// /// ...but it truncates of Q is too small.
    /// assert_eq!(abc.concat(defg), tinystr!(6, "abcdef"));
    /// assert_eq!(abc.concat(defg), tinystr!(2, "ab"));
    /// ```
    pub const fn concat<const M: usize, const Q: usize>(
        self,
        other: TinyAsciiStr<M>,
    ) -> TinyAsciiStr<Q> {
        let mut result = self.resize::<Q>();
        let mut i = self.len();
        let mut j = 0;
        // Indexing is protected by the loop guard
        #[expect(clippy::indexing_slicing)]
        while i < Q && j < M {
            result.bytes[i] = other.bytes[j];
            i += 1;
            j += 1;
        }
        result
    }

    /// # Safety
    /// Must be called with a bytes array made of valid ASCII bytes, with no null bytes
    /// between ASCII characters
    #[must_use]
    pub const unsafe fn from_utf8_unchecked(code_units: [u8; N]) -> Self {
        Self {
            bytes: AsciiByte::to_ascii_byte_array(&code_units),
        }
    }
}

macro_rules! check_is {
    ($self:ident, $check_int:ident, $check_u8:ident) => {
        if N <= 4 {
            Aligned4::from_ascii_bytes(&$self.bytes).$check_int()
        } else if N <= 8 {
            Aligned8::from_ascii_bytes(&$self.bytes).$check_int()
        } else {
            let mut i = 0;
            while i < N && $self.bytes[i] as u8 != AsciiByte::B0 as u8 {
                if !($self.bytes[i] as u8).$check_u8() {
                    return false;
                }
                i += 1;
            }
            true
        }
    };
    ($self:ident, $check_int:ident, !$check_u8_0_inv:ident, !$check_u8_1_inv:ident) => {
        if N <= 4 {
            Aligned4::from_ascii_bytes(&$self.bytes).$check_int()
        } else if N <= 8 {
            Aligned8::from_ascii_bytes(&$self.bytes).$check_int()
        } else {
            // Won't panic because N is > 8
            if ($self.bytes[0] as u8).$check_u8_0_inv() {
                return false;
            }
            let mut i = 1;
            while i < N && $self.bytes[i] as u8 != AsciiByte::B0 as u8 {
                if ($self.bytes[i] as u8).$check_u8_1_inv() {
                    return false;
                }
                i += 1;
            }
            true
        }
    };
    ($self:ident, $check_int:ident, $check_u8_0_inv:ident, $check_u8_1_inv:ident) => {
        if N <= 4 {
            Aligned4::from_ascii_bytes(&$self.bytes).$check_int()
        } else if N <= 8 {
            Aligned8::from_ascii_bytes(&$self.bytes).$check_int()
        } else {
            // Won't panic because N is > 8
            if !($self.bytes[0] as u8).$check_u8_0_inv() {
                return false;
            }
            let mut i = 1;
            while i < N && $self.bytes[i] as u8 != AsciiByte::B0 as u8 {
                if !($self.bytes[i] as u8).$check_u8_1_inv() {
                    return false;
                }
                i += 1;
            }
            true
        }
    };
}

impl<const N: usize> TinyAsciiStr<N> {
    /// Checks if the value is composed of ASCII alphabetic characters:
    ///
    ///  * U+0041 'A' ..= U+005A 'Z', or
    ///  * U+0061 'a' ..= U+007A 'z'.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "Test".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "Te3t".parse().expect("Failed to parse.");
    ///
    /// assert!(s1.is_ascii_alphabetic());
    /// assert!(!s2.is_ascii_alphabetic());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_alphabetic(&self) -> bool {
        check_is!(self, is_ascii_alphabetic, is_ascii_alphabetic)
    }

    /// Checks if the value is composed of ASCII alphanumeric characters:
    ///
    ///  * U+0041 'A' ..= U+005A 'Z', or
    ///  * U+0061 'a' ..= U+007A 'z', or
    ///  * U+0030 '0' ..= U+0039 '9'.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "A15b".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "[3@w".parse().expect("Failed to parse.");
    ///
    /// assert!(s1.is_ascii_alphanumeric());
    /// assert!(!s2.is_ascii_alphanumeric());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_alphanumeric(&self) -> bool {
        check_is!(self, is_ascii_alphanumeric, is_ascii_alphanumeric)
    }

    /// Checks if the value is composed of ASCII decimal digits:
    ///
    ///  * U+0030 '0' ..= U+0039 '9'.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "312".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "3d".parse().expect("Failed to parse.");
    ///
    /// assert!(s1.is_ascii_numeric());
    /// assert!(!s2.is_ascii_numeric());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_numeric(&self) -> bool {
        check_is!(self, is_ascii_numeric, is_ascii_digit)
    }

    /// Checks if the value is in ASCII lower case.
    ///
    /// All letter characters are checked for case. Non-letter characters are ignored.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "test".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(!s1.is_ascii_lowercase());
    /// assert!(s2.is_ascii_lowercase());
    /// assert!(s3.is_ascii_lowercase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_lowercase(&self) -> bool {
        check_is!(
            self,
            is_ascii_lowercase,
            !is_ascii_uppercase,
            !is_ascii_uppercase
        )
    }

    /// Checks if the value is in ASCII title case.
    ///
    /// This verifies that the first character is ASCII uppercase and all others ASCII lowercase.
    /// Non-letter characters are ignored.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "Test".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(!s1.is_ascii_titlecase());
    /// assert!(s2.is_ascii_titlecase());
    /// assert!(s3.is_ascii_titlecase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_titlecase(&self) -> bool {
        check_is!(
            self,
            is_ascii_titlecase,
            !is_ascii_lowercase,
            !is_ascii_uppercase
        )
    }

    /// Checks if the value is in ASCII upper case.
    ///
    /// All letter characters are checked for case. Non-letter characters are ignored.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "TEST".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(!s1.is_ascii_uppercase());
    /// assert!(s2.is_ascii_uppercase());
    /// assert!(!s3.is_ascii_uppercase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_uppercase(&self) -> bool {
        check_is!(
            self,
            is_ascii_uppercase,
            !is_ascii_lowercase,
            !is_ascii_lowercase
        )
    }

    /// Checks if the value is composed of ASCII alphabetic lower case characters:
    ///
    ///  * U+0061 'a' ..= U+007A 'z',
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "Test".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "Te3t".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s4: TinyAsciiStr<4> = "test".parse().expect("Failed to parse.");
    /// let s5: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(!s1.is_ascii_alphabetic_lowercase());
    /// assert!(!s2.is_ascii_alphabetic_lowercase());
    /// assert!(!s3.is_ascii_alphabetic_lowercase());
    /// assert!(s4.is_ascii_alphabetic_lowercase());
    /// assert!(!s5.is_ascii_alphabetic_lowercase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_alphabetic_lowercase(&self) -> bool {
        check_is!(
            self,
            is_ascii_alphabetic_lowercase,
            is_ascii_lowercase,
            is_ascii_lowercase
        )
    }

    /// Checks if the value is composed of ASCII alphabetic, with the first character being ASCII uppercase, and all others ASCII lowercase.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "Test".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "Te3t".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s4: TinyAsciiStr<4> = "test".parse().expect("Failed to parse.");
    /// let s5: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(s1.is_ascii_alphabetic_titlecase());
    /// assert!(!s2.is_ascii_alphabetic_titlecase());
    /// assert!(!s3.is_ascii_alphabetic_titlecase());
    /// assert!(!s4.is_ascii_alphabetic_titlecase());
    /// assert!(!s5.is_ascii_alphabetic_titlecase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_alphabetic_titlecase(&self) -> bool {
        check_is!(
            self,
            is_ascii_alphabetic_titlecase,
            is_ascii_uppercase,
            is_ascii_lowercase
        )
    }

    /// Checks if the value is composed of ASCII alphabetic upper case characters:
    ///
    ///  * U+0041 'A' ..= U+005A 'Z',
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "Test".parse().expect("Failed to parse.");
    /// let s2: TinyAsciiStr<4> = "Te3t".parse().expect("Failed to parse.");
    /// let s3: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    /// let s4: TinyAsciiStr<4> = "TEST".parse().expect("Failed to parse.");
    /// let s5: TinyAsciiStr<4> = "001z".parse().expect("Failed to parse.");
    ///
    /// assert!(!s1.is_ascii_alphabetic_uppercase());
    /// assert!(!s2.is_ascii_alphabetic_uppercase());
    /// assert!(!s3.is_ascii_alphabetic_uppercase());
    /// assert!(s4.is_ascii_alphabetic_uppercase());
    /// assert!(!s5.is_ascii_alphabetic_uppercase());
    /// ```
    #[inline]
    #[must_use]
    pub const fn is_ascii_alphabetic_uppercase(&self) -> bool {
        check_is!(
            self,
            is_ascii_alphabetic_uppercase,
            is_ascii_uppercase,
            is_ascii_uppercase
        )
    }
}

macro_rules! to {
    ($self:ident, $to:ident, $later_char_to:ident $(,$first_char_to:ident)?) => {{
        let mut i = 0;
        if N <= 4 {
            let aligned = Aligned4::from_ascii_bytes(&$self.bytes).$to();
            // Won't panic because self.bytes has length N and aligned has length >= N
            #[expect(clippy::indexing_slicing)]
            while i < N {
                $self.bytes[i] = aligned[i];
                i += 1;
            }
        } else if N <= 8 {
            let aligned = Aligned8::from_ascii_bytes(&$self.bytes).$to();
            // Won't panic because self.bytes has length N and aligned has length >= N
            #[expect(clippy::indexing_slicing)]
            while i < N {
                $self.bytes[i] = aligned[i];
                i += 1;
            }
        } else {
            while i < N && $self.bytes[i] as u8 != AsciiByte::B0 as u8 {
                $self.bytes[i] = $self.bytes[i].$later_char_to();
                i += 1;
            }
            $(
                $self.bytes[0] = $self.bytes[0].$first_char_to();
            )?
        }
        $self
    }};
}

impl<const N: usize> TinyAsciiStr<N> {
    /// Converts this type to its ASCII lower case equivalent in-place.
    ///
    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z', other characters are unchanged.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "TeS3".parse().expect("Failed to parse.");
    ///
    /// assert_eq!(&*s1.to_ascii_lowercase(), "tes3");
    /// ```
    #[inline]
    #[must_use]
    pub const fn to_ascii_lowercase(mut self) -> Self {
        to!(self, to_ascii_lowercase, to_ascii_lowercase)
    }

    /// Converts this type to its ASCII title case equivalent in-place.
    ///
    /// The first character is converted to ASCII uppercase; the remaining characters
    /// are converted to ASCII lowercase.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "teSt".parse().expect("Failed to parse.");
    ///
    /// assert_eq!(&*s1.to_ascii_titlecase(), "Test");
    /// ```
    #[inline]
    #[must_use]
    pub const fn to_ascii_titlecase(mut self) -> Self {
        to!(
            self,
            to_ascii_titlecase,
            to_ascii_lowercase,
            to_ascii_uppercase
        )
    }

    /// Converts this type to its ASCII upper case equivalent in-place.
    ///
    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z', other characters are unchanged.
    ///
    /// # Examples
    ///
    /// ```
    /// use tinystr::TinyAsciiStr;
    ///
    /// let s1: TinyAsciiStr<4> = "Tes3".parse().expect("Failed to parse.");
    ///
    /// assert_eq!(&*s1.to_ascii_uppercase(), "TES3");
    /// ```
    #[inline]
    #[must_use]
    pub const fn to_ascii_uppercase(mut self) -> Self {
        to!(self, to_ascii_uppercase, to_ascii_uppercase)
    }
}

impl<const N: usize> fmt::Debug for TinyAsciiStr<N> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(self.as_str(), f)
    }
}

impl<const N: usize> fmt::Display for TinyAsciiStr<N> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(self.as_str(), f)
    }
}

impl<const N: usize> Deref for TinyAsciiStr<N> {
    type Target = str;
    #[inline]
    fn deref(&self) -> &str {
        self.as_str()
    }
}

impl<const N: usize> Borrow<str> for TinyAsciiStr<N> {
    #[inline]
    fn borrow(&self) -> &str {
        self.as_str()
    }
}

impl<const N: usize> FromStr for TinyAsciiStr<N> {
    type Err = ParseError;
    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::try_from_str(s)
    }
}

impl<const N: usize> PartialEq<str> for TinyAsciiStr<N> {
    fn eq(&self, other: &str) -> bool {
        self.deref() == other
    }
}

impl<const N: usize> PartialEq<&str> for TinyAsciiStr<N> {
    fn eq(&self, other: &&str) -> bool {
        self.deref() == *other
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> PartialEq<String> for TinyAsciiStr<N> {
    fn eq(&self, other: &String) -> bool {
        self.deref() == other.deref()
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> PartialEq<TinyAsciiStr<N>> for String {
    fn eq(&self, other: &TinyAsciiStr<N>) -> bool {
        self.deref() == other.deref()
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use rand::distr::Distribution;
    use rand::distr::StandardUniform;
    use rand::rngs::SmallRng;
    use rand::SeedableRng;

    const STRINGS: [&str; 26] = [
        "Latn",
        "laTn",
        "windows",
        "AR",
        "Hans",
        "macos",
        "AT",
        "infiniband",
        "FR",
        "en",
        "Cyrl",
        "FromIntegral",
        "NO",
        "419",
        "MacintoshOSX2019",
        "a3z",
        "A3z",
        "A3Z",
        "a3Z",
        "3A",
        "3Z",
        "3a",
        "3z",
        "@@[`{",
        "UK",
        "E12",
    ];

    fn gen_strings(num_strings: usize, allowed_lengths: &[usize]) -> Vec<String> {
        use rand::seq::IndexedRandom;
        let mut rng = SmallRng::seed_from_u64(2022);
        // Need to do this in 2 steps since the RNG is needed twice
        let string_lengths = core::iter::repeat_with(|| *allowed_lengths.choose(&mut rng).unwrap())
            .take(num_strings)
            .collect::<Vec<usize>>();
        string_lengths
            .iter()
            .map(|len| {
                StandardUniform
                    .sample_iter(&mut rng)
                    .filter(|b: &u8| *b > 0 && *b < 0x80)
                    .take(*len)
                    .collect::<Vec<u8>>()
            })
            .map(|byte_vec| String::from_utf8(byte_vec).expect("All ASCII"))
            .collect()
    }

    fn check_operation<T, F1, F2, const N: usize>(reference_f: F1, tinystr_f: F2)
    where
        F1: Fn(&str) -> T,
        F2: Fn(TinyAsciiStr<N>) -> T,
        T: fmt::Debug + PartialEq,
    {
        for s in STRINGS
            .into_iter()
            .map(str::to_owned)
            .chain(gen_strings(100, &[3, 4, 5, 8, 12]))
        {
            let t = match TinyAsciiStr::<N>::from_str(&s) {
                Ok(t) => t,
                Err(ParseError::TooLong { .. }) => continue,
                Err(e) => panic!("{}", e),
            };
            let expected = reference_f(&s);
            let actual = tinystr_f(t);
            assert_eq!(expected, actual, "TinyAsciiStr<{N}>: {s:?}");

            let s_utf16: Vec<u16> = s.encode_utf16().collect();
            let t = match TinyAsciiStr::<N>::try_from_utf16(&s_utf16) {
                Ok(t) => t,
                Err(ParseError::TooLong { .. }) => continue,
                Err(e) => panic!("{}", e),
            };
            let expected = reference_f(&s);
            let actual = tinystr_f(t);
            assert_eq!(expected, actual, "TinyAsciiStr<{N}>: {s:?}");
        }
    }

    #[test]
    fn test_is_ascii_alphabetic() {
        fn check<const N: usize>() {
            check_operation(
                |s| s.chars().all(|c| c.is_ascii_alphabetic()),
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_alphabetic(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_alphanumeric() {
        fn check<const N: usize>() {
            check_operation(
                |s| s.chars().all(|c| c.is_ascii_alphanumeric()),
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_alphanumeric(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_numeric() {
        fn check<const N: usize>() {
            check_operation(
                |s| s.chars().all(|c| c.is_ascii_digit()),
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_numeric(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_lowercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_lowercase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_lowercase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_titlecase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_titlecase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_titlecase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_uppercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_uppercase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_uppercase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_alphabetic_lowercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    // Check alphabetic
                    s.chars().all(|c| c.is_ascii_alphabetic()) &&
                    // Check lowercase
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_lowercase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_alphabetic_lowercase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_alphabetic_titlecase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    // Check alphabetic
                    s.chars().all(|c| c.is_ascii_alphabetic()) &&
                    // Check titlecase
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_titlecase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_alphabetic_titlecase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_is_ascii_alphabetic_uppercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    // Check alphabetic
                    s.chars().all(|c| c.is_ascii_alphabetic()) &&
                    // Check uppercase
                    s == TinyAsciiStr::<16>::try_from_str(s)
                        .unwrap()
                        .to_ascii_uppercase()
                        .as_str()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::is_ascii_alphabetic_uppercase(&t),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_to_ascii_lowercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    s.chars()
                        .map(|c| c.to_ascii_lowercase())
                        .collect::<String>()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::to_ascii_lowercase(t).as_str().to_owned(),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_to_ascii_titlecase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    let mut r = s
                        .chars()
                        .map(|c| c.to_ascii_lowercase())
                        .collect::<String>();
                    // Safe because the string is nonempty and an ASCII string
                    unsafe { r.as_bytes_mut()[0].make_ascii_uppercase() };
                    r
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::to_ascii_titlecase(t).as_str().to_owned(),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn test_to_ascii_uppercase() {
        fn check<const N: usize>() {
            check_operation(
                |s| {
                    s.chars()
                        .map(|c| c.to_ascii_uppercase())
                        .collect::<String>()
                },
                |t: TinyAsciiStr<N>| TinyAsciiStr::to_ascii_uppercase(t).as_str().to_owned(),
            )
        }
        check::<2>();
        check::<3>();
        check::<4>();
        check::<5>();
        check::<8>();
        check::<16>();
    }

    #[test]
    fn lossy_constructor() {
        assert_eq!(TinyAsciiStr::<4>::from_utf8_lossy(b"", b'?').as_str(), "");
        assert_eq!(
            TinyAsciiStr::<4>::from_utf8_lossy(b"oh\0o", b'?').as_str(),
            "oh?o"
        );
        assert_eq!(
            TinyAsciiStr::<4>::from_utf8_lossy(b"\0", b'?').as_str(),
            "?"
        );
        assert_eq!(
            TinyAsciiStr::<4>::from_utf8_lossy(b"toolong", b'?').as_str(),
            "tool"
        );
        assert_eq!(
            TinyAsciiStr::<4>::from_utf8_lossy(&[b'a', 0x80, 0xFF, b'1'], b'?').as_str(),
            "a??1"
        );
    }

    #[test]
    #[should_panic(expected = "replacement must be a non-null ASCII byte")]
    fn from_utf8_lossy_rejects_non_ascii_replacement() {
        // A non-ASCII replacement byte (>= 0x80) would create an invalid AsciiByte
        // discriminant and then from_utf8_unchecked would be called on non-UTF-8
        // data (UB). The fix validates the replacement byte on entry.
        let _ = TinyAsciiStr::<4>::from_utf8_lossy(b"\xFF", 0xFF);
    }

    #[test]
    #[should_panic(expected = "replacement must be a non-null ASCII byte")]
    fn from_utf16_lossy_rejects_non_ascii_replacement() {
        let _ = TinyAsciiStr::<4>::from_utf16_lossy(&[0xFFFF], 0xFF);
    }

    #[test]
    #[should_panic(expected = "replacement must be a non-null ASCII byte")]
    fn from_utf8_lossy_rejects_null_replacement() {
        // Null (0x00) is also invalid — it's the TinyAsciiStr terminator.
        let _ = TinyAsciiStr::<4>::from_utf8_lossy(b"\xFF", 0x00);
    }
}