uuid/

fmt.rs

// Copyright 2013-2014 The Rust Project Developers.
// Copyright 2018 The Uuid Project Developers.
//
// See the COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Adapters for alternative string formats.

use core::{mem::MaybeUninit, ptr, slice, str::FromStr};

use crate::{
    std::{borrow::Borrow, fmt, str},
    Error, Uuid, Variant,
};

#[cfg(feature = "std")]
use crate::std::string::{String, ToString};

impl std::fmt::Debug for Uuid {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::LowerHex::fmt(self, f)
    }
}

impl fmt::Display for Uuid {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::LowerHex::fmt(self, f)
    }
}

#[cfg(feature = "std")]
impl From<Uuid> for String {
    fn from(uuid: Uuid) -> Self {
        uuid.to_string()
    }
}

impl fmt::Display for Variant {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Variant::NCS => write!(f, "NCS"),
            Variant::RFC4122 => write!(f, "RFC4122"),
            Variant::Microsoft => write!(f, "Microsoft"),
            Variant::Future => write!(f, "Future"),
        }
    }
}

impl fmt::LowerHex for Uuid {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::LowerHex::fmt(self.as_hyphenated(), f)
    }
}

impl fmt::UpperHex for Uuid {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::UpperHex::fmt(self.as_hyphenated(), f)
    }
}

/// Format a [`Uuid`] as a hyphenated string, like
/// `67e55044-10b1-426f-9247-bb680e5fe0c8`.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[cfg_attr(
    all(uuid_unstable, feature = "zerocopy"),
    derive(
        zerocopy::IntoBytes,
        zerocopy::FromBytes,
        zerocopy::KnownLayout,
        zerocopy::Immutable,
        zerocopy::Unaligned
    )
)]
#[repr(transparent)]
pub struct Hyphenated(Uuid);

/// Format a [`Uuid`] as a simple string, like
/// `67e5504410b1426f9247bb680e5fe0c8`.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[cfg_attr(
    all(uuid_unstable, feature = "zerocopy"),
    derive(
        zerocopy::IntoBytes,
        zerocopy::FromBytes,
        zerocopy::KnownLayout,
        zerocopy::Immutable,
        zerocopy::Unaligned
    )
)]
#[repr(transparent)]
pub struct Simple(Uuid);

/// Format a [`Uuid`] as a URN string, like
/// `urn:uuid:67e55044-10b1-426f-9247-bb680e5fe0c8`.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[cfg_attr(
    all(uuid_unstable, feature = "zerocopy"),
    derive(
        zerocopy::IntoBytes,
        zerocopy::FromBytes,
        zerocopy::KnownLayout,
        zerocopy::Immutable,
        zerocopy::Unaligned
    )
)]
#[repr(transparent)]
pub struct Urn(Uuid);

/// Format a [`Uuid`] as a braced hyphenated string, like
/// `{67e55044-10b1-426f-9247-bb680e5fe0c8}`.
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[cfg_attr(
    all(uuid_unstable, feature = "zerocopy"),
    derive(
        zerocopy::IntoBytes,
        zerocopy::FromBytes,
        zerocopy::KnownLayout,
        zerocopy::Immutable,
        zerocopy::Unaligned
    )
)]
#[repr(transparent)]
pub struct Braced(Uuid);

impl Uuid {
    /// Get a [`Hyphenated`] formatter.
    #[inline]
    pub const fn hyphenated(self) -> Hyphenated {
        Hyphenated(self)
    }

    /// Get a borrowed [`Hyphenated`] formatter.
    #[inline]
    pub fn as_hyphenated(&self) -> &Hyphenated {
        unsafe_transmute_ref!(self)
    }

    /// Get a [`Simple`] formatter.
    #[inline]
    pub const fn simple(self) -> Simple {
        Simple(self)
    }

    /// Get a borrowed [`Simple`] formatter.
    #[inline]
    pub fn as_simple(&self) -> &Simple {
        unsafe_transmute_ref!(self)
    }

    /// Get a [`Urn`] formatter.
    #[inline]
    pub const fn urn(self) -> Urn {
        Urn(self)
    }

    /// Get a borrowed [`Urn`] formatter.
    #[inline]
    pub fn as_urn(&self) -> &Urn {
        unsafe_transmute_ref!(self)
    }

    /// Get a [`Braced`] formatter.
    #[inline]
    pub const fn braced(self) -> Braced {
        Braced(self)
    }

    /// Get a borrowed [`Braced`] formatter.
    #[inline]
    pub fn as_braced(&self) -> &Braced {
        unsafe_transmute_ref!(self)
    }
}

// Maps a hex nibble (0..=15) to its ASCII character. `alpha_offset` is added
// for values above 9: 0x27 for lowercase, 0x07 for uppercase.
#[inline]
const fn nibble_to_hex(nibble: u8, alpha_offset: u8) -> u8 {
    nibble + b'0' + if nibble > 9 { alpha_offset } else { 0 }
}

#[inline]
const fn format_simple(src: &[u8; 16], upper: bool) -> [u8; 32] {
    let alpha_offset = if upper { 0x07 } else { 0x27 };
    let mut dst = [0; 32];
    let mut i = 0;
    while i < 16 {
        let x = src[i];
        dst[i * 2] = nibble_to_hex(x >> 4, alpha_offset);
        dst[i * 2 + 1] = nibble_to_hex(x & 0x0f, alpha_offset);
        i += 1;
    }
    dst
}

#[inline]
const fn format_hyphenated(src: &[u8; 16], upper: bool) -> [u8; 36] {
    let simple = format_simple(src, upper);
    let mut dst = [0; 36];

    let mut i = 0;
    while i < 8 {
        dst[i] = simple[i];
        i += 1;
    }
    dst[8] = b'-';
    while i < 12 {
        dst[i + 1] = simple[i];
        i += 1;
    }
    dst[13] = b'-';
    while i < 16 {
        dst[i + 2] = simple[i];
        i += 1;
    }
    dst[18] = b'-';
    while i < 20 {
        dst[i + 3] = simple[i];
        i += 1;
    }
    dst[23] = b'-';
    while i < 32 {
        dst[i + 4] = simple[i];
        i += 1;
    }
    dst
}

#[inline]
fn encode_simple<'b>(src: &[u8; 16], buffer: &'b mut [u8], upper: bool) -> &'b mut str {
    let buf = &mut buffer[..Simple::LENGTH];

    encode_simple_uninit(src, slice_as_uninit_mut(buf), upper)
}

#[inline]
fn encode_hyphenated<'b>(src: &[u8; 16], buffer: &'b mut [u8], upper: bool) -> &'b mut str {
    let buf = &mut buffer[..Hyphenated::LENGTH];

    encode_hyphenated_uninit(src, slice_as_uninit_mut(buf), upper)
}

#[inline]
fn encode_braced<'b>(src: &[u8; 16], buffer: &'b mut [u8], upper: bool) -> &'b mut str {
    let buf = &mut buffer[..Hyphenated::LENGTH + 2];

    encode_braced_uninit(src, slice_as_uninit_mut(buf), upper)
}

#[inline]
fn encode_urn<'b>(src: &[u8; 16], buffer: &'b mut [u8], upper: bool) -> &'b mut str {
    let buf = &mut buffer[..Urn::LENGTH];

    encode_urn_uninit(src, slice_as_uninit_mut(buf), upper)
}

#[inline]
fn encode_simple_uninit<'b>(
    src: &[u8; 16],
    buffer: &'b mut [MaybeUninit<u8>],
    upper: bool,
) -> &'b mut str {
    let buf = &mut buffer[..Simple::LENGTH];
    write_bytes(buf, &format_simple(src, upper));

    // SAFETY: The encoded buffer is fully initialized and ASCII encoded.
    unsafe { assume_init_ascii_mut(buf) }
}

#[inline]
fn encode_hyphenated_uninit<'b>(
    src: &[u8; 16],
    buffer: &'b mut [MaybeUninit<u8>],
    upper: bool,
) -> &'b mut str {
    let buf = &mut buffer[..Hyphenated::LENGTH];
    write_bytes(buf, &format_hyphenated(src, upper));

    // SAFETY: The encoded buffer is fully initialized and ASCII encoded.
    unsafe { assume_init_ascii_mut(buf) }
}

#[inline]
fn encode_braced_uninit<'b>(
    src: &[u8; 16],
    buffer: &'b mut [MaybeUninit<u8>],
    upper: bool,
) -> &'b mut str {
    let buf = &mut buffer[..Hyphenated::LENGTH + 2];

    #[cfg_attr(all(uuid_unstable, feature = "zerocopy"), derive(zerocopy::IntoBytes))]
    #[repr(C)]
    struct BracedBytes {
        open_curly: u8,
        hyphenated: [u8; Hyphenated::LENGTH],
        close_curly: u8,
    }

    let braced = BracedBytes {
        open_curly: b'{',
        hyphenated: format_hyphenated(src, upper),
        close_curly: b'}',
    };
    let braced: [u8; Hyphenated::LENGTH + 2] = unsafe_transmute!(braced);

    write_bytes(buf, &braced);

    // SAFETY: The encoded buffer is fully initialized and ASCII encoded.
    unsafe { assume_init_ascii_mut(buf) }
}

#[inline]
fn encode_urn_uninit<'b>(
    src: &[u8; 16],
    buffer: &'b mut [MaybeUninit<u8>],
    upper: bool,
) -> &'b mut str {
    let buf = &mut buffer[..Urn::LENGTH];
    write_bytes(&mut buf[..9], b"urn:uuid:");

    let dst = &mut buf[9..(9 + Hyphenated::LENGTH)];
    write_bytes(dst, &format_hyphenated(src, upper));

    // SAFETY: The encoded buffer is fully initialized and ASCII encoded.
    unsafe { assume_init_ascii_mut(buf) }
}

#[inline]
fn write_bytes(dst: &mut [MaybeUninit<u8>], src: &[u8]) {
    debug_assert_eq!(dst.len(), src.len());
    let dst = &mut dst[..src.len()];

    // SAFETY: `dst` and `src` are distinct slices, and `dst` has been sliced to
    // the same length as `src`. `MaybeUninit<u8>` has the same layout as `u8`.
    unsafe {
        ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr().cast(), src.len());
    }
}

#[inline]
fn slice_as_uninit_mut(buffer: &mut [u8]) -> &mut [MaybeUninit<u8>] {
    // SAFETY: `MaybeUninit<u8>` has the same layout as `u8`.
    unsafe { slice::from_raw_parts_mut(buffer.as_mut_ptr().cast(), buffer.len()) }
}

#[inline]
unsafe fn assume_init_ascii_mut(buffer: &mut [MaybeUninit<u8>]) -> &mut str {
    // SAFETY: The caller guarantees that `buffer` has been initialized.
    let buffer = unsafe { slice::from_raw_parts_mut(buffer.as_mut_ptr().cast(), buffer.len()) };

    // SAFETY: The caller guarantees that `buffer` is ASCII encoded.
    unsafe { str::from_utf8_unchecked_mut(buffer) }
}

impl Hyphenated {
    /// The length of a hyphenated [`Uuid`] string.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    pub const LENGTH: usize = 36;

    /// Creates a [`Hyphenated`] from a [`Uuid`].
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    /// [`Hyphenated`]: struct.Hyphenated.html
    pub const fn from_uuid(uuid: Uuid) -> Self {
        Hyphenated(uuid)
    }

    /// Writes the [`Uuid`] as a lower-case hyphenated string to
    /// `buffer`, and returns the subslice of the buffer that contains the
    /// encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936DA01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.hyphenated()
    ///             .encode_lower(&mut Uuid::encode_buffer()),
    ///         "936da01f-9abd-4d9d-80c7-02af85c822a8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 40];
    ///     uuid.hyphenated().encode_lower(&mut buf);
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"936da01f-9abd-4d9d-80c7-02af85c822a8!!!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_lower<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_hyphenated(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as a lower-case hyphenated string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_lower_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_hyphenated_uninit(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as an upper-case hyphenated string to
    /// `buffer`, and returns the subslice of the buffer that contains the
    /// encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936da01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.hyphenated()
    ///             .encode_upper(&mut Uuid::encode_buffer()),
    ///         "936DA01F-9ABD-4D9D-80C7-02AF85C822A8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 40];
    ///     uuid.hyphenated().encode_upper(&mut buf);
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"936DA01F-9ABD-4D9D-80C7-02AF85C822A8!!!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_upper<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_hyphenated(self.0.as_bytes(), buffer, true)
    }

    /// Writes the [`Uuid`] as an upper-case hyphenated string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_upper_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_hyphenated_uninit(self.0.as_bytes(), buffer, true)
    }

    /// Get a reference to the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let hyphenated = Uuid::nil().hyphenated();
    /// assert_eq!(*hyphenated.as_uuid(), Uuid::nil());
    /// ```
    pub const fn as_uuid(&self) -> &Uuid {
        &self.0
    }

    /// Consumes the [`Hyphenated`], returning the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let hyphenated = Uuid::nil().hyphenated();
    /// assert_eq!(hyphenated.into_uuid(), Uuid::nil());
    /// ```
    pub const fn into_uuid(self) -> Uuid {
        self.0
    }
}

impl Braced {
    /// The length of a braced [`Uuid`] string.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    pub const LENGTH: usize = 38;

    /// Creates a [`Braced`] from a [`Uuid`].
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    /// [`Braced`]: struct.Braced.html
    pub const fn from_uuid(uuid: Uuid) -> Self {
        Braced(uuid)
    }

    /// Writes the [`Uuid`] as a lower-case hyphenated string surrounded by
    /// braces to `buffer`, and returns the subslice of the buffer that contains
    /// the encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936DA01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.braced()
    ///             .encode_lower(&mut Uuid::encode_buffer()),
    ///         "{936da01f-9abd-4d9d-80c7-02af85c822a8}"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 40];
    ///     uuid.braced().encode_lower(&mut buf);
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"{936da01f-9abd-4d9d-80c7-02af85c822a8}!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_lower<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_braced(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as a lower-case hyphenated string surrounded by
    /// braces to a possibly-uninitialized `buffer`, and returns the subslice of
    /// the buffer that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_lower_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_braced_uninit(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as an upper-case hyphenated string surrounded by
    /// braces to `buffer`, and returns the subslice of the buffer that contains
    /// the encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936da01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.braced()
    ///             .encode_upper(&mut Uuid::encode_buffer()),
    ///         "{936DA01F-9ABD-4D9D-80C7-02AF85C822A8}"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 40];
    ///     uuid.braced().encode_upper(&mut buf);
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"{936DA01F-9ABD-4D9D-80C7-02AF85C822A8}!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_upper<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_braced(self.0.as_bytes(), buffer, true)
    }

    /// Writes the [`Uuid`] as an upper-case hyphenated string surrounded by
    /// braces to a possibly-uninitialized `buffer`, and returns the subslice of
    /// the buffer that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_upper_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_braced_uninit(self.0.as_bytes(), buffer, true)
    }

    /// Get a reference to the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let braced = Uuid::nil().braced();
    /// assert_eq!(*braced.as_uuid(), Uuid::nil());
    /// ```
    pub const fn as_uuid(&self) -> &Uuid {
        &self.0
    }

    /// Consumes the [`Braced`], returning the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let braced = Uuid::nil().braced();
    /// assert_eq!(braced.into_uuid(), Uuid::nil());
    /// ```
    pub const fn into_uuid(self) -> Uuid {
        self.0
    }
}

impl Simple {
    /// The length of a simple [`Uuid`] string.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    pub const LENGTH: usize = 32;

    /// Creates a [`Simple`] from a [`Uuid`].
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    /// [`Simple`]: struct.Simple.html
    pub const fn from_uuid(uuid: Uuid) -> Self {
        Simple(uuid)
    }

    /// Writes the [`Uuid`] as a lower-case simple string to `buffer`,
    /// and returns the subslice of the buffer that contains the encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936DA01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.simple().encode_lower(&mut Uuid::encode_buffer()),
    ///         "936da01f9abd4d9d80c702af85c822a8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 36];
    ///     assert_eq!(
    ///         uuid.simple().encode_lower(&mut buf),
    ///         "936da01f9abd4d9d80c702af85c822a8"
    ///     );
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"936da01f9abd4d9d80c702af85c822a8!!!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_lower<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_simple(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as a lower-case simple string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_lower_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_simple_uninit(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as an upper-case simple string to `buffer`,
    /// and returns the subslice of the buffer that contains the encoded UUID.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936da01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.simple().encode_upper(&mut Uuid::encode_buffer()),
    ///         "936DA01F9ABD4D9D80C702AF85C822A8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 36];
    ///     assert_eq!(
    ///         uuid.simple().encode_upper(&mut buf),
    ///         "936DA01F9ABD4D9D80C702AF85C822A8"
    ///     );
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"936DA01F9ABD4D9D80C702AF85C822A8!!!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_upper<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_simple(self.0.as_bytes(), buffer, true)
    }

    /// Writes the [`Uuid`] as an upper-case simple string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_upper_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_simple_uninit(self.0.as_bytes(), buffer, true)
    }

    /// Get a reference to the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let simple = Uuid::nil().simple();
    /// assert_eq!(*simple.as_uuid(), Uuid::nil());
    /// ```
    pub const fn as_uuid(&self) -> &Uuid {
        &self.0
    }

    /// Consumes the [`Simple`], returning the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let simple = Uuid::nil().simple();
    /// assert_eq!(simple.into_uuid(), Uuid::nil());
    /// ```
    pub const fn into_uuid(self) -> Uuid {
        self.0
    }
}

impl Urn {
    /// The length of a URN [`Uuid`] string.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    pub const LENGTH: usize = 45;

    /// Creates a [`Urn`] from a [`Uuid`].
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    /// [`Urn`]: struct.Urn.html
    pub const fn from_uuid(uuid: Uuid) -> Self {
        Urn(uuid)
    }

    /// Writes the [`Uuid`] as a lower-case URN string to
    /// `buffer`, and returns the subslice of the buffer that contains the
    /// encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936DA01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.urn().encode_lower(&mut Uuid::encode_buffer()),
    ///         "urn:uuid:936da01f-9abd-4d9d-80c7-02af85c822a8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 49];
    ///     uuid.urn().encode_lower(&mut buf);
    ///     assert_eq!(
    ///         uuid.urn().encode_lower(&mut buf),
    ///         "urn:uuid:936da01f-9abd-4d9d-80c7-02af85c822a8"
    ///     );
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"urn:uuid:936da01f-9abd-4d9d-80c7-02af85c822a8!!!!" as &[_]
    ///     );
    ///     
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_lower<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_urn(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as a lower-case URN string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_lower_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_urn_uninit(self.0.as_bytes(), buffer, false)
    }

    /// Writes the [`Uuid`] as an upper-case URN string to
    /// `buffer`, and returns the subslice of the buffer that contains the
    /// encoded UUID.
    ///
    /// This is slightly more efficient than using the formatting
    /// infrastructure as it avoids virtual calls, and may avoid
    /// double buffering.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`]. [`Uuid::encode_buffer`] can be used to get a
    /// sufficiently-large temporary buffer.
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    /// [`Uuid::encode_buffer`]: ../struct.Uuid.html#method.encode_buffer
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// fn main() -> Result<(), uuid::Error> {
    ///     let uuid = Uuid::parse_str("936da01f9abd4d9d80c702af85c822a8")?;
    ///
    ///     // the encoded portion is returned
    ///     assert_eq!(
    ///         uuid.urn().encode_upper(&mut Uuid::encode_buffer()),
    ///         "urn:uuid:936DA01F-9ABD-4D9D-80C7-02AF85C822A8"
    ///     );
    ///
    ///     // the buffer is mutated directly, and trailing contents remains
    ///     let mut buf = [b'!'; 49];
    ///     assert_eq!(
    ///         uuid.urn().encode_upper(&mut buf),
    ///         "urn:uuid:936DA01F-9ABD-4D9D-80C7-02AF85C822A8"
    ///     );
    ///     assert_eq!(
    ///         &buf as &[_],
    ///         b"urn:uuid:936DA01F-9ABD-4D9D-80C7-02AF85C822A8!!!!" as &[_]
    ///     );
    ///
    ///     Ok(())
    /// }
    /// ```
    /// */
    #[inline]
    pub fn encode_upper<'buf>(&self, buffer: &'buf mut [u8]) -> &'buf mut str {
        encode_urn(self.0.as_bytes(), buffer, true)
    }

    /// Writes the [`Uuid`] as an upper-case URN string to a
    /// possibly-uninitialized `buffer`, and returns the subslice of the buffer
    /// that contains the encoded UUID.
    ///
    /// This initializes the returned subslice of `buffer`. Bytes outside of the
    /// returned subslice are not written.
    ///
    /// [`Uuid`]: ../struct.Uuid.html
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough: it must have length at least
    /// [`LENGTH`].
    ///
    /// [`LENGTH`]: #associatedconstant.LENGTH
    #[inline]
    pub fn encode_upper_uninit<'buf>(&self, buffer: &'buf mut [MaybeUninit<u8>]) -> &'buf mut str {
        encode_urn_uninit(self.0.as_bytes(), buffer, true)
    }

    /// Get a reference to the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let urn = Uuid::nil().urn();
    /// assert_eq!(*urn.as_uuid(), Uuid::nil());
    /// ```
    pub const fn as_uuid(&self) -> &Uuid {
        &self.0
    }

    /// Consumes the [`Urn`], returning the underlying [`Uuid`].
    ///
    /// # Examples
    ///
    /// ```rust
    /// use uuid::Uuid;
    ///
    /// let urn = Uuid::nil().urn();
    /// assert_eq!(urn.into_uuid(), Uuid::nil());
    /// ```
    pub const fn into_uuid(self) -> Uuid {
        self.0
    }
}

impl FromStr for Hyphenated {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        crate::parser::parse_hyphenated(s.as_bytes())
            .map(|b| Hyphenated(Uuid(b)))
            .map_err(|invalid| invalid.into_err())
    }
}

impl FromStr for Simple {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        crate::parser::parse_simple(s.as_bytes(), false)
            .map(|b| Simple(Uuid(b)))
            .map_err(|invalid| invalid.into_err())
    }
}

impl FromStr for Urn {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        crate::parser::parse_urn(s.as_bytes())
            .map(|b| Urn(Uuid(b)))
            .map_err(|invalid| invalid.into_err())
    }
}

impl FromStr for Braced {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        crate::parser::parse_braced(s.as_bytes())
            .map(|b| Braced(Uuid(b)))
            .map_err(|invalid| invalid.into_err())
    }
}

macro_rules! impl_fmt_traits {
    ($($T:ident<$($a:lifetime),*>),+) => {$(
        impl<$($a),*> fmt::Display for $T<$($a),*> {
            #[inline]
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                fmt::LowerHex::fmt(self, f)
            }
        }

        impl<$($a),*> fmt::LowerHex for $T<$($a),*> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                f.write_str(self.encode_lower(&mut [0; Self::LENGTH]))
            }
        }

        impl<$($a),*> fmt::UpperHex for $T<$($a),*> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                f.write_str(self.encode_upper(&mut [0; Self::LENGTH]))
            }
        }

        impl_fmt_from!($T<$($a),*>);
    )+}
}

macro_rules! impl_fmt_from {
    ($T:ident<>) => {
        impl From<Uuid> for $T {
            #[inline]
            fn from(f: Uuid) -> Self {
                $T(f)
            }
        }

        impl From<$T> for Uuid {
            #[inline]
            fn from(f: $T) -> Self {
                f.into_uuid()
            }
        }

        impl AsRef<Uuid> for $T {
            #[inline]
            fn as_ref(&self) -> &Uuid {
                &self.0
            }
        }

        impl Borrow<Uuid> for $T {
            #[inline]
            fn borrow(&self) -> &Uuid {
                &self.0
            }
        }
    };
    ($T:ident<$a:lifetime>) => {
        impl<$a> From<&$a Uuid> for $T<$a> {
            #[inline]
            fn from(f: &$a Uuid) -> Self {
                $T::from_uuid_ref(f)
            }
        }

        impl<$a> From<$T<$a>> for &$a Uuid {
            #[inline]
            fn from(f: $T<$a>) -> &$a Uuid {
                f.0
            }
        }

        impl<$a> AsRef<Uuid> for $T<$a> {
            #[inline]
            fn as_ref(&self) -> &Uuid {
                self.0
            }
        }

        impl<$a> Borrow<Uuid> for $T<$a> {
            #[inline]
            fn borrow(&self) -> &Uuid {
                self.0
            }
        }
    };
}

impl_fmt_traits! {
    Hyphenated<>,
    Simple<>,
    Urn<>,
    Braced<>
}

#[cfg(test)]
mod tests {
    use super::*;

    use core::mem::MaybeUninit;

    #[test]
    fn encode_lower_uninit() {
        let uuid = Uuid::parse_str("936DA01f9abd4d9d80c702af85c822a8").unwrap();

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.hyphenated().encode_lower_uninit(&mut buf);
            assert_eq!(encoded, "936da01f-9abd-4d9d-80c7-02af85c822a8");
            encoded.len()
        };
        assert_eq!(len, Hyphenated::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.simple().encode_lower_uninit(&mut buf);
            assert_eq!(encoded, "936da01f9abd4d9d80c702af85c822a8");
            encoded.len()
        };
        assert_eq!(len, Simple::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.urn().encode_lower_uninit(&mut buf);
            assert_eq!(encoded, "urn:uuid:936da01f-9abd-4d9d-80c7-02af85c822a8");
            encoded.len()
        };
        assert_eq!(len, Urn::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.braced().encode_lower_uninit(&mut buf);
            assert_eq!(encoded, "{936da01f-9abd-4d9d-80c7-02af85c822a8}");
            encoded.len()
        };
        assert_eq!(len, Braced::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);
    }

    #[test]
    fn encode_upper_uninit() {
        let uuid = Uuid::parse_str("936da01f9abd4d9d80c702af85c822a8").unwrap();

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.hyphenated().encode_upper_uninit(&mut buf);
            assert_eq!(encoded, "936DA01F-9ABD-4D9D-80C7-02AF85C822A8");
            encoded.len()
        };
        assert_eq!(len, Hyphenated::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.simple().encode_upper_uninit(&mut buf);
            assert_eq!(encoded, "936DA01F9ABD4D9D80C702AF85C822A8");
            encoded.len()
        };
        assert_eq!(len, Simple::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.urn().encode_upper_uninit(&mut buf);
            assert_eq!(encoded, "urn:uuid:936DA01F-9ABD-4D9D-80C7-02AF85C822A8");
            encoded.len()
        };
        assert_eq!(len, Urn::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);

        let mut buf = [MaybeUninit::new(b'x'); 100];
        let len = {
            let encoded = uuid.braced().encode_upper_uninit(&mut buf);
            assert_eq!(encoded, "{936DA01F-9ABD-4D9D-80C7-02AF85C822A8}");
            encoded.len()
        };
        assert_eq!(len, Braced::LENGTH);
        assert_uninit_tail_unchanged(&buf, len);
    }

    fn assert_uninit_tail_unchanged(buffer: &[MaybeUninit<u8>], initialized: usize) {
        // SAFETY: The test initializes the full buffer before encoding.
        let buffer: &[u8] =
            unsafe { core::slice::from_raw_parts(buffer.as_ptr().cast(), buffer.len()) };

        assert!(buffer[initialized..].iter().all(|b| *b == b'x'));
    }

    #[test]
    fn hyphenated_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().hyphenated().encode_lower(&mut buf).len();
        assert_eq!(len, super::Hyphenated::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn hyphenated_ref_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().as_hyphenated().encode_lower(&mut buf).len();
        assert_eq!(len, super::Hyphenated::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn simple_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().simple().encode_lower(&mut buf).len();
        assert_eq!(len, super::Simple::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn simple_ref_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().as_simple().encode_lower(&mut buf).len();
        assert_eq!(len, super::Simple::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn urn_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().urn().encode_lower(&mut buf).len();
        assert_eq!(len, super::Urn::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn urn_ref_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().as_urn().encode_lower(&mut buf).len();
        assert_eq!(len, super::Urn::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn braced_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().braced().encode_lower(&mut buf).len();
        assert_eq!(len, super::Braced::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    fn braced_ref_trailing() {
        let mut buf = [b'x'; 100];
        let len = Uuid::nil().as_braced().encode_lower(&mut buf).len();
        assert_eq!(len, super::Braced::LENGTH);
        assert!(buf[len..].iter().all(|x| *x == b'x'));
    }

    #[test]
    #[should_panic]
    fn hyphenated_too_small() {
        Uuid::nil().hyphenated().encode_lower(&mut [0; 35]);
    }

    #[test]
    #[should_panic]
    fn simple_too_small() {
        Uuid::nil().simple().encode_lower(&mut [0; 31]);
    }

    #[test]
    #[should_panic]
    fn urn_too_small() {
        Uuid::nil().urn().encode_lower(&mut [0; 44]);
    }

    #[test]
    #[should_panic]
    fn braced_too_small() {
        Uuid::nil().braced().encode_lower(&mut [0; 37]);
    }

    #[test]
    fn hyphenated_to_inner() {
        let hyphenated = Uuid::nil().hyphenated();
        assert_eq!(Uuid::from(hyphenated), Uuid::nil());
    }

    #[test]
    fn simple_to_inner() {
        let simple = Uuid::nil().simple();
        assert_eq!(Uuid::from(simple), Uuid::nil());
    }

    #[test]
    fn urn_to_inner() {
        let urn = Uuid::nil().urn();
        assert_eq!(Uuid::from(urn), Uuid::nil());
    }

    #[test]
    fn braced_to_inner() {
        let braced = Uuid::nil().braced();
        assert_eq!(Uuid::from(braced), Uuid::nil());
    }
}