tiny_str/

lib.rs

/*  Copyright (C) 2025 Saúl Valdelvira
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, version 3.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>. */

//! Tiny string
//!
//! A string that can store a small amount of bytes on the stack.
//!
//! This struct provides a string-like API, but performs SSO (Small String Optimization)
//! This means that a `TinyString<N>` stores up to N bytes on the stack.
//! If the string grows bigger than that, it moves the contents to the heap.
//!
#![cfg_attr(not(feature = "alloc"), doc = "
# WARNING
The `alloc` feature is disabled. This means that a `TinyString` won't be able to
grow over it's stack capacity.

The following functions from [TinyString] can cause the program to panic if the string
exceeds its capacity.
- [with_capacity]
- [repeat](TinyString::repeat)
- [push]
- [push_str]
- [reserve]
- [reserve_exact]
- [extend_from_within](TinyString::extend_from_within)
- [insert](TinyString::insert)
- [insert_str](TinyString::insert_str)

## Alternatives
| May Panic | No Panic |
| --------- | -------- |
|  [push]   | [push_within_capacity](TinyString::push_within_capacity) |
|  [push_str]   | [push_within_capacity](TinyString::push_str_within_capacity) |
|  [reserve]   | [try_reserve](TinyString::try_reserve) |
| [with_capacity] | [try_with_capacity](TinyString::try_with_capacity) |
| [reserve] | [try_reserve](TinyString::try_reserve) |
| [reserve_exact] | [try_reserve_exact](TinyString::try_reserve_exact) |

[push]: TinyString::push
[push_str]: TinyString::push_str
[reserve]: TinyString::reserve
[reserve_exact]: TinyString::reserve_exact
[with_capacity]: TinyString::with_capacity
")]
//!
//! # Example
//! ```
//! use tiny_str::TinyString;
//!
//! let mut s = TinyString::<10>::new();
//!
//! for (i, c) in (b'0'..=b'9').enumerate() {
//!     s.push(c as char);
//!     assert_eq!(s.len(), i + 1);
//! }
//!
//! // Up to this point, no heap allocations are needed.
//! // The string is stored on the stack.
//!
//! s.push_str("abc"); // This moves the string to the heap
//!
//! assert_eq!(&s[..], "0123456789abc")
//! ```
//!
//! # Memory layout
//! [TinyString] is based on [TinyVec], just like [String] is based on [Vec].
//!
//! You can read the [tiny_vec] crate documentation to learn about the internal
//! representation of the data.
//!
#![cfg_attr(not(feature = "alloc"), doc = "
[String]: <https://doc.rust-lang.org/alloc/string/struct.String.html>
[Vec]: <https://doc.rust-lang.org/alloc/vec/struct.Vec.html>")]

#![no_std]

#![cfg_attr(feature = "use-nightly-features", feature(extend_one))]

use core::fmt::{self, Display};
use core::hash::Hash;
use core::ops::{AddAssign, Bound, Deref, DerefMut, Range, RangeBounds};
use core::str::{self, FromStr, Utf8Error};

#[cfg(feature = "alloc")]
extern crate alloc;
#[cfg(feature = "alloc")]
use alloc::{
    vec::Vec,
    boxed::Box,
    string::String,
};

use tiny_vec::TinyVec;
pub use tiny_vec::ResizeError;
pub mod iter;

pub mod drain;

mod cow;
pub use cow::Cow;

const MAX_N_STACK_ELEMENTS: usize = tiny_vec::n_elements_for_stack::<u8>();

/// A string that can store a small amount of bytes on the stack.
pub struct TinyString<const N: usize = MAX_N_STACK_ELEMENTS> {
    buf: TinyVec<u8, N>,
}

impl<const N: usize> TinyString<N> {
    fn slice_range<R>(&self, range: R, len: usize) -> Range<usize>
    where
        R: RangeBounds<usize>
    {
        let start = match range.start_bound() {
            Bound::Included(n) => *n,
            Bound::Excluded(n) => *n + 1,
            Bound::Unbounded => 0,
        };

        let end = match range.end_bound() {
            Bound::Included(n) => *n + 1,
            Bound::Excluded(n) => *n,
            Bound::Unbounded => len,
        };

        assert!(start <= end);
        assert!(end <= len);
        assert!(self.is_char_boundary(start));
        assert!(self.is_char_boundary(end));

        Range { start, end }
    }
}

impl<const N: usize> TinyString<N> {

    /// Creates a new [TinyString]
    #[inline]
    #[must_use]
    pub const fn new() -> Self {
        Self { buf: TinyVec::new() }
    }

    /// Creates a new [TinyString] with the given capacity
    #[must_use]
    pub fn with_capacity(cap: usize) -> Self {
        Self { buf: TinyVec::with_capacity(cap) }
    }

    /// Like [with_capacity](Self::with_capacity), but it returns a [Result].
    ///
    /// If an allocation error hapens when reserving the memory, returns
    /// a [ResizeError] unlike [with_capacity](Self::with_capacity), which
    /// panics in such case.
    pub fn try_with_capacity(cap: usize) -> Result<Self,ResizeError> {
        Ok(Self { buf: TinyVec::try_with_capacity(cap)? })
    }

    /// Creates a new [TinyString] from the given utf8 buffer.
    ///
    /// # Errors
    /// If the byte buffer contains invalid uft8
    pub fn from_utf8(utf8: TinyVec<u8, N>) -> Result<Self,Utf8Error> {
        str::from_utf8(utf8.as_slice())?;
        Ok(Self { buf: utf8 })
    }

    /// Creates a new [TinyString] from the given utf8 buffer.
    ///
    /// # Safety
    /// The caller must ensure that the given contains valid utf8
    #[inline(always)]
    #[must_use]
    pub const unsafe fn from_utf8_unchecked(utf8: TinyVec<u8, N>) -> Self {
        Self { buf: utf8 }
    }

    /// Creates a new `TinyString` by repeating the given `slice` `n` times.
    ///
    /// # Panics
    /// If the capacity requires overflows `isize::MAX`
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    /// let s = TinyString::<10>::repeat("abc", 5);
    /// assert_eq!(s.as_str(), "abcabcabcabcabc");
    /// ```
    #[must_use]
    pub fn repeat(slice: &str, n: usize) -> Self {
        Self {
            buf: TinyVec::repeat(slice.as_bytes(), n)
        }
    }

    /// Returns the number of elements inside this string
    #[inline]
    pub const fn len(&self) -> usize { self.buf.len() }

    /// Returns true if the string is empty
    #[inline]
    pub const fn is_empty(&self) -> bool { self.buf.is_empty() }

    /// Returns the allocated capacity for this string
    #[inline]
    pub const fn capacity(&self) -> usize { self.buf.capacity() }

    /// Returns true if the string is currently using stack memory.
    ///
    /// This means that [Self::len] <= `N`
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut vec = TinyString::<5>::new();
    ///
    /// for n in 0..5 {
    ///     vec.push('a')
    /// }
    ///
    /// assert!(vec.lives_on_stack());
    /// vec.push('a');
    /// assert!(!vec.lives_on_stack());
    /// ```
    #[inline]
    pub const fn lives_on_stack(&self) -> bool { self.buf.lives_on_stack() }

    /// Returns a str slice
    #[inline]
    pub const fn as_str(&self) -> &str {
        unsafe { str::from_utf8_unchecked(self.buf.as_slice()) }
    }

    /// Returns a mutable str slice
    #[inline]
    pub const fn as_mut_str(&mut self) -> &mut str {
        unsafe { str::from_utf8_unchecked_mut(self.buf.as_mut_slice()) }
    }

    /// Returns a const pointer to the buffer
    ///
    /// This method shadows [str::as_ptr], to avoid a deref
    #[inline]
    pub const fn as_ptr(&self) -> *const u8 {
        self.buf.as_ptr()
    }

    /// Returns a mutable pointer to the buffer
    ///
    /// This method shadows [str::as_mut_ptr], to avoid a deref
    #[inline]
    pub const fn as_mut_ptr(&mut self) -> *mut u8 {
        self.buf.as_mut_ptr()
    }

    /// Returns the string as a byte slice
    #[inline]
    pub const fn as_bytes(&self) -> &[u8] {
        self.buf.as_slice()
    }

    /// Returns the string as a byte slice
    ///
    /// Returns the string as a mutable bytes slice
    ///
    /// # Safety
    /// Modifying this byte slice is dangerous, because it can leave the
    /// buffer on an inconsistent state.
    /// Strings must be valid UTF8. So manually changing the byte contents
    /// of the string could lead to bugs.
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<10>::from("hello");
    /// unsafe {
    ///     let slice = s.as_mut_bytes();
    ///     assert_eq!(&[104, 101, 108, 108, 111][..], &slice[..]);
    ///     slice.reverse();
    /// }
    /// assert_eq!(s, "olleh");
    /// ```
    #[inline]
    pub const unsafe fn as_mut_bytes(&mut self) -> &mut [u8] {
        self.buf.as_mut_slice()
    }

    /// Returns a mutable reference to the contents of this `TinyString`
    ///
    /// # Safety
    /// Modifying this [TinyVec] is dangerous, because it can leave the
    /// buffer on an inconsistent state.
    /// Strings must be valid UTF8. So mutating the vector without respecting
    /// that could lead to bugs.
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<10>::from("hello");
    /// unsafe {
    ///     let vec = s.as_mut_vec();
    ///     assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
    ///     vec.drain(1..3);
    /// }
    /// assert_eq!(s, "hlo");
    /// ```
    #[inline]
    pub const unsafe fn as_mut_vec(&mut self) -> &mut TinyVec<u8, N> {
        &mut self.buf
    }

    /// Pushes a character into the string
    pub fn push(&mut self, c: char) {
        let len = c.len_utf8();
        if len == 1 {
            self.buf.push(c as u8);
        } else {
            let mut buf = [0_u8; 4];
            c.encode_utf8(&mut buf);
            self.buf.copy_from_slice(&buf[..len]);
        }
    }

    /// Tries to push a character. If the string doesn't have enough capacity to store
    /// the new char, returns an [Err] variant.
    ///
    /// # Errors
    /// If pushing the character would've caused the buffer to grow.
    pub fn push_within_capacity(&mut self, c: char) -> Result<(), char> {
        let len = c.len_utf8();
        if self.buf.len() + len > self.buf.capacity() {
            return Err(c)
        }
        if len == 1 {
            unsafe { self.buf.push_unchecked(c as u8) };
        } else {
            let mut buf = [0_u8; 4];
            c.encode_utf8(&mut buf);
            self.buf.copy_from_slice(&buf[..len]);
        }
        Ok(())
    }


    /// Returns the last char of this string, if present
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<10>::new();
    ///
    /// s.push_str("abcd");
    ///
    /// assert_eq!(s.pop(), Some('d'));
    /// assert_eq!(s, "abc");
    /// ```
    pub fn pop(&mut self) -> Option<char> {
        let c = self.chars().next_back()?;
        let new_len = self.len() - c.len_utf8();
        unsafe {
            self.buf.set_len(new_len);
        }
        Some(c)
    }

    /// Pushes a str slice into this string
    #[inline]
    pub fn push_str(&mut self, s: &str) {
        self.buf.copy_from_slice(s.as_bytes());
    }

    /// Tries to push a str slice. If this `TinyString` doesn't have enough
    /// capacity to store the new slice, returns an [Err] variant.
    ///
    /// # Errors
    /// If pushing the string would've caused the buffer to grow.
    pub fn push_str_within_capacity<'a>(&mut self, s: &'a str) -> Result<(), &'a str> {
        if self.buf.len() + s.len() > self.buf.capacity() {
            Err(s)
        } else {
            self.buf.copy_from_slice(s.as_bytes());
            Ok(())
        }
    }
    /// Shrinks the capacity of this `String` with a lower bound.
    ///
    /// The capacity will remain at least as large as both the length
    /// and the supplied value.
    ///
    /// If the current capacity is less than the lower limit, this is a no-op.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<5>::from("foobar");
    ///
    /// s.reserve(100);
    /// assert!(s.capacity() >= 100);
    ///
    /// s.shrink_to(10);
    /// assert!(s.capacity() >= 10, "{}", s.capacity());
    /// s.shrink_to(0);
    /// assert!(s.capacity() >= 6);
    /// ```
    #[inline]
    #[cfg(feature = "alloc")]
    pub fn shrink_to(&mut self, min_capacity: usize) {
        self.buf.shrink_to(min_capacity)
    }

    /// Shrinks the capacity of `self` to match its length.
    ///
    /// # Examples
    /// ```
    /// use tiny_str::TinyString;
    /// let mut s = TinyString::<5>::from("foobar");
    ///
    /// s.reserve(100);
    /// assert!(s.capacity() >= 100);
    ///
    /// s.shrink_to_fit();
    /// assert_eq!(6, s.capacity());
    /// ```
    #[inline]
    #[cfg(feature = "alloc")]
    pub fn shrink_to_fit(&mut self) {
        self.buf.shrink_to_fit();
    }

    /// Clears the string
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s: TinyString<5> = TinyString::from("Hello");
    /// s.clear();
    ///
    /// assert!(s.is_empty());
    /// assert_eq!(s.as_str(), "");
    /// ```
    #[inline]
    pub fn clear(&mut self) {
        self.buf.clear();
    }

    /// Reserves space for, at least, n bytes
    #[inline]
    pub fn reserve(&mut self, n: usize) {
        self.buf.reserve(n);
    }

    /// Like [reserve](Self::reserve), but on failure returns an [Err] variant
    /// with a [ResizeError], instead of panicking.
    #[inline]
    pub fn try_reserve(&mut self, n: usize) -> Result<(), ResizeError> {
        self.buf.try_reserve(n)
    }

    /// Reserves space for exactly n more bytes
    #[inline]
    pub fn reserve_exact(&mut self, n: usize) {
        self.buf.reserve_exact(n);
    }

    /// Like [reserve_exact](Self::reserve_exact), but on failure returns an [Err] variant
    /// with a [ResizeError], instead of panicking.
    #[inline]
    pub fn try_reserve_exact(&mut self, n: usize) -> Result<(), ResizeError> {
        self.buf.try_reserve_exact(n)
    }

    /// Converts this TinyString into a boxed str
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<10>::new();
    /// s.push_str("abc");
    ///
    /// let b = s.into_boxed_str();
    /// assert_eq!(&*b, "abc");
    /// ```
    #[cfg(feature = "alloc")]
    #[must_use]
    pub fn into_boxed_str(self) -> Box<str> {
        let b = self.buf.into_boxed_slice();
        unsafe { alloc::str::from_boxed_utf8_unchecked(b) }
    }

    /// Copies the slice from the given range to the back
    /// of this string.
    ///
    /// # Panics
    /// - If the range is invalid for [0, self.len)
    /// - If either the start or the end of the range fall
    ///   outside a char boundary
    ///
    /// # Example
    /// ```
    /// use tiny_str::TinyString;
    ///
    /// let mut s = TinyString::<10>::from("abcdefg");
    ///
    /// s.extend_from_within(3..=5);
    ///
    /// assert_eq!(s, "abcdefgdef");
    /// ```
    pub fn extend_from_within<R>(&mut self, range: R)
    where
        R: RangeBounds<usize>
    {
        let Range { start, end } = self.slice_range(range, self.len());
        self.buf.extend_from_within_copied(start..end);
    }

    /// Consumes and leaks the `TinyString`, returning a mutable reference to the contents,
    /// `&'a mut str`.
    ///
    /// This method shrinks the buffer, and moves it to the heap in case it lived
    /// on the stack.
    ///
    /// This function is mainly useful for data that lives for the remainder of
    /// the program's life. Dropping the returned reference will cause a memory
    /// leak.
    ///
    /// # Example
    /// ```
    /// let x = tiny_str::TinyString::<10>::from("ABCDEFG");
    ///
    /// let static_ref: &'static mut str = x.leak();
    /// static_ref.make_ascii_lowercase();
    ///
    /// assert_eq!(static_ref, "abcdefg");
    /// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
    /// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
    /// # drop(unsafe{Box::from_raw(static_ref)})
    /// ```
    #[cfg(feature = "alloc")]
    pub fn leak<'a>(mut self) -> &'a mut str {
        self.buf.move_to_heap_exact();
        self.buf.shrink_to_fit_heap_only();
        unsafe {
            let bytes = self.buf.leak();
            str::from_utf8_unchecked_mut(bytes)
        }
    }

    /// Splits the string into two at the given byte index.
    ///
    /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
    /// the returned `String` contains bytes `[at, len)`. `at` must be on the
    /// boundary of a UTF-8 code point.
    ///
    /// Note that the capacity of `self` does not change.
    ///
    /// # Panics
    ///
    /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
    /// code point of the string.
    ///
    /// # Examples
    /// ```
    /// let mut hello = tiny_str::TinyString::<8>::from("Hello, World!");
    /// let world = hello.split_off(7);
    /// assert_eq!(hello, "Hello, ");
    /// assert_eq!(world, "World!");
    /// ```
    #[inline]
    #[must_use = "use `.truncate()` if you don't need the other half"]
    pub fn split_off(&mut self, at: usize) -> TinyString<N> {
        assert!(self.is_char_boundary(at));
        let other = self.buf.split_off(at);
        unsafe { TinyString::from_utf8_unchecked(other) }
    }

    /// Shortens this `TinyString` to the specified length.
    ///
    /// If `new_len` is greater than or equal to the string's current length, this has no
    /// effect.
    ///
    /// Note that this method has no effect on the allocated capacity
    /// of the string
    ///
    /// # Panics
    ///
    /// Panics if `new_len` does not lie on a [`char`] boundary.
    ///
    /// # Example
    /// ```
    /// let mut s = tiny_str::TinyString::<6>::from("hello");
    ///
    /// s.truncate(2);
    ///
    /// assert_eq!(s, "he");
    /// ```
    pub fn truncate(&mut self, new_len: usize) {
        assert!(self.is_char_boundary(new_len));
        self.buf.truncate(new_len);
    }

    /// Inserts a character into this `TinyString` at a byte position.
    ///
    /// This is an *O*(*n*) operation as it requires copying every element in the
    /// buffer.
    ///
    /// # Panics
    ///
    /// Panics if `index` is larger than the `TinyString`'s length, or if it does not
    /// lie on a [`char`] boundary.
    ///
    /// # Example
    /// ```
    /// let mut s = tiny_str::TinyString::<10>::from("Hello world :)");
    ///
    /// s.insert(5, '@');
    ///
    /// assert_eq!(s, "Hello@ world :)");
    /// ```
    pub fn insert(&mut self, index: usize, ch: char) {
        assert!(self.is_char_boundary(index));
        let mut buf = [0; 4];
        ch.encode_utf8(&mut buf);
        let len = ch.len_utf8();
        self.buf.insert_slice(index, &buf[..len]).unwrap_or_else(|_| {
            unreachable!("We've checked the index in the assertion above")
        })
    }

    /// Inserts a string slice into this `TinyString` at a byte position.
    ///
    /// This is an *O*(*n*) operation as it requires copying every element in the
    /// buffer.
    ///
    /// # Panics
    ///
    /// Panics if `index` is larger than the `TinyString`'s length, or if it does not
    /// lie on a [`char`] boundary.
    ///
    /// # Example
    /// ```
    /// let mut s = tiny_str::TinyString::<8>::from("Heworld");
    ///
    /// s.insert_str(2, "llo ");
    ///
    /// assert_eq!("Hello world", s);
    /// ```
    pub fn insert_str(&mut self, index: usize, s: &str) {
        assert!(self.is_char_boundary(index));
        self.buf.insert_slice(index, s.as_bytes()).unwrap_or_else(|_| {
            unreachable!("We've checked the index in the assertion above")
        })
    }
}

impl<const N: usize> Default for TinyString<N> {
    fn default() -> Self {
        Self::new()
    }
}

impl<const N: usize> Deref for TinyString<N> {
    type Target = str;

    fn deref(&self) -> &Self::Target {
        self.as_str()
    }
}

impl<const N: usize> DerefMut for TinyString<N> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.as_mut_str()
    }
}

impl<const N: usize> From<&str> for TinyString<N> {
    fn from(value: &str) -> Self {
        let mut s = Self::with_capacity(value.len());
        s.push_str(value);
        s
    }
}

impl<const N: usize> TryFrom<&[u8]> for TinyString<N> {
    type Error = Utf8Error;

    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
        str::from_utf8(value)?;
        Ok(unsafe { Self::from_utf8_unchecked(TinyVec::from_slice_copied(value)) })
    }
}

impl<const N: usize> TryFrom<TinyVec<u8, N>> for TinyString<N> {
    type Error = Utf8Error;

    fn try_from(value: TinyVec<u8, N>) -> Result<Self, Self::Error> {
        Self::from_utf8(value)
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> TryFrom<Vec<u8>> for TinyString<N> {
    type Error = Utf8Error;

    fn try_from(value: Vec<u8>) -> Result<Self, Self::Error> {
        str::from_utf8(value.as_slice())?;
        Ok(unsafe { Self::from_utf8_unchecked(TinyVec::from_vec(value)) })
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> From<String> for TinyString<N> {
    fn from(value: String) -> Self {
        let vec = Vec::from(value);
        let vec = TinyVec::<_, N>::from_vec(vec);
        unsafe { Self::from_utf8_unchecked(vec) }
    }
}

impl<const N: usize> From<TinyString<N>> for TinyVec<u8, N> {
    fn from(value: TinyString<N>) -> Self {
        value.buf
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> From<TinyString<N>> for Vec<u8> {
    fn from(value: TinyString<N>) -> Self {
        value.buf.into_vec()
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> From<TinyString<N>> for Box<str> {
    fn from(value: TinyString<N>) -> Self {
        value.into_boxed_str()
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> From<Box<str>> for TinyString<N> {
    fn from(value: Box<str>) -> Self {
        let vec = value.as_bytes();
        let s = TinyVec::from(vec);
        unsafe { Self::from_utf8_unchecked(s) }
    }
}

macro_rules! impl_from_iter {
    ($( $( { $($tok:tt)* } )? $t:ty),* $(,)?) => {
        $(
            impl< $($($tok)*, )? const N: usize> FromIterator<$t> for TinyString<N> {
                fn from_iter<T: IntoIterator<Item = $t>>(iter: T) -> Self {
                    let mut s = Self::new();
                    s.extend(iter);
                    s
                }
            }
        )*
    };
}

impl_from_iter!(
    char,
    {'a} &'a char,
    {'a} &'a str,
    {'a, const M: usize} Cow<'a, M>
);

#[cfg(feature = "alloc")]
impl_from_iter!(Box<str>);

impl<const N: usize> Extend<char> for TinyString<N> {
    fn extend<T: IntoIterator<Item = char>>(&mut self, iter: T) {
        let iter = iter.into_iter();
        let (lower, _) = iter.size_hint();
        self.reserve(lower);
        for c in iter {
            self.push(c);
        }
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_one(&mut self, item: char) {
        self.push(item);
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_reserve(&mut self, additional: usize) {
        self.reserve(additional);
    }
}

impl<'a, const N: usize> Extend<&'a char> for TinyString<N> {
    fn extend<T: IntoIterator<Item = &'a char>>(&mut self, iter: T) {
        iter.into_iter().for_each(|slice| self.push(*slice));
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_one(&mut self, item: &'a char) {
        self.push(*item);
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_reserve(&mut self, additional: usize) {
        self.reserve(additional);
    }
}

impl<'a, const N: usize> Extend<&'a str> for TinyString<N> {
    fn extend<T: IntoIterator<Item = &'a str>>(&mut self, iter: T) {
        iter.into_iter().for_each(|slice| self.push_str(slice));
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_one(&mut self, item: &'a str) {
        self.push_str(item);
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> Extend<Box<str>> for TinyString<N> {
    fn extend<T: IntoIterator<Item = Box<str>>>(&mut self, iter: T) {
        iter.into_iter().for_each(|slice| self.push_str(&slice));
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_one(&mut self, item: Box<str>) {
        self.push_str(&item);
    }
}

impl<'a, const N: usize, const M: usize> Extend<Cow<'a, M>> for TinyString<N> {
    fn extend<T: IntoIterator<Item = Cow<'a, M>>>(&mut self, iter: T) {
        iter.into_iter().for_each(|slice| self.push_str(&slice));
    }

    #[cfg(feature = "use-nightly-features")]
    #[inline]
    fn extend_one(&mut self, item: Cow<'a, M>) {
        self.push_str(&item);
    }
}

impl<const N: usize, const M: usize> PartialEq<TinyString<M>> for TinyString<N> {
    fn eq(&self, other: &TinyString<M>) -> bool {
        self.as_bytes() == other.as_bytes()
    }
}

impl<const N: usize> Eq for TinyString<N> { }

impl<'a, const N: usize, const M: usize> PartialEq<Cow<'a, M>> for TinyString<N> {
    fn eq(&self, other: &Cow<'a, M>) -> bool {
        self.as_bytes() == other.as_bytes()
    }
}

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

impl<const N: usize, const M: usize> PartialEq<TinyVec<u8, M>> for TinyString<N> {
    fn eq(&self, other: &TinyVec<u8, M>) -> bool {
        self.as_bytes() == other.as_slice()
    }
}

impl<'a, const N: usize, const M: usize> PartialEq<tiny_vec::Cow<'a, u8, M>> for TinyString<N> {
    fn eq(&self, other: &tiny_vec::Cow<'a, u8, M>) -> bool {
        self.as_bytes() == other.as_slice()
    }
}

#[cfg(feature = "alloc")]
impl<const N: usize> PartialEq<Vec<u8>> for TinyString<N> {
    fn eq(&self, other: &Vec<u8>) -> bool {
        self.as_bytes() == other.as_slice()
    }
}

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

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

impl<const N: usize> PartialEq<[u8]> for TinyString<N> {
    fn eq(&self, other: &[u8]) -> bool {
        self.as_bytes() == other
    }
}

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

impl<const N: usize> PartialOrd<TinyString<N>> for TinyString<N> {
    #[inline]
    fn partial_cmp(&self, other: &TinyString<N>) -> Option<core::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl<const N: usize> Ord for TinyString<N> {
    #[inline]
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        self.buf.cmp(&other.buf)
    }
}

impl<const N: usize> Clone for TinyString<N> {
    #[inline]
    fn clone(&self) -> Self {
        Self { buf: self.buf.clone() }
    }

    #[inline]
    fn clone_from(&mut self, source: &Self) {
        self.buf.clone_from(&source.buf);
    }
}

impl<const N: usize> AsRef<[u8]> for TinyString<N> {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.as_bytes()
    }
}

impl<const N: usize> AsRef<str> for TinyString<N> {
    #[inline]
    fn as_ref(&self) -> &str {
        self.as_str()
    }
}

impl<const N: usize> AsMut<str> for TinyString<N> {
    #[inline]
    fn as_mut(&mut self) -> &mut str {
        self.as_mut_str()
    }
}

impl<const N: usize> AsRef<TinyString<N>> for TinyString<N> {
    #[inline]
    fn as_ref(&self) -> &TinyString<N> {
        self
    }
}

impl<const N: usize> AsMut<TinyString<N>> for TinyString<N> {
    #[inline]
    fn as_mut(&mut self) -> &mut TinyString<N> {
        self
    }
}

impl<const N: usize> Hash for TinyString<N> {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.buf.hash(state);
    }
}

impl<const N: usize> fmt::Debug for TinyString<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "{:?}", self.bytes())
    }
}

impl<const N: usize> Display for TinyString<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "{}", self.as_str())
    }
}

impl<const N: usize> FromStr for TinyString<N> {
    type Err = core::convert::Infallible;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Ok(Self::from(s))
    }
}

impl<const N: usize> core::fmt::Write for TinyString<N> {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.push_str(s);
        Ok(())
    }

    fn write_char(&mut self, c: char) -> fmt::Result {
        self.push(c);
        Ok(())
    }
}

impl<'a, const N: usize> AddAssign<&'a str> for TinyString<N> {
    #[inline]
    fn add_assign(&mut self, rhs: &'a str) {
        self.push_str(rhs);
    }
}

#[cfg(feature = "serde")]
impl<const N: usize> serde::Serialize for TinyString<N> {
    #[inline]
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer
    {
        self.buf.serialize(serializer)
    }
}

#[cfg(feature = "serde")]
impl<'de, const N: usize> serde::Deserialize<'de> for TinyString<N> {
    #[inline]
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>
    {
        let buf = TinyVec::<u8, N>::deserialize(deserializer)?;
        Ok(Self { buf })
    }
}

#[cfg(test)]
mod test;