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    use std::fmt::Debug;
    use std::hash::Hash;

    use error::{Error, Result};

    // NOTE: Most of this code was copied from regex-automata, but without the
    // (de)serialization specific stuff.

    /// Check that the premultiplication of the given state identifier can
    /// fit into the representation indicated by `S`. If it cannot, or if it
    /// overflows `usize` itself, then an error is returned.
    pub fn premultiply_overflow_error<S: StateID>(
        last_state: S,
        alphabet_len: usize,
    ) -> Result<()> {
        let requested = match last_state.to_usize().checked_mul(alphabet_len) {
            Some(requested) => requested,
            None => return Err(Error::premultiply_overflow(0, 0)),
        };
        if requested > S::max_id() {
            return Err(Error::premultiply_overflow(S::max_id(), requested));
        }
        Ok(())
    }

    /// Convert the given `usize` to the chosen state identifier
    /// representation. If the given value cannot fit in the chosen
    /// representation, then an error is returned.
    pub fn usize_to_state_id<S: StateID>(value: usize) -> Result<S> {
        if value > S::max_id() {
            Err(Error::state_id_overflow(S::max_id()))
        } else {
            Ok(S::from_usize(value))
        }
    }

    /// Return the unique identifier for an automaton's fail state in the chosen
    /// representation indicated by `S`.
    pub fn fail_id<S: StateID>() -> S {
        S::from_usize(0)
    }

    /// Return the unique identifier for an automaton's fail state in the chosen
    /// representation indicated by `S`.
    pub fn dead_id<S: StateID>() -> S {
        S::from_usize(1)
    }

    mod private {
        /// Sealed stops crates other than aho-corasick from implementing any
        /// traits that use it.
        pub trait Sealed{}
        impl Sealed for u8 {}
        impl Sealed for u16 {}
        impl Sealed for u32 {}
        impl Sealed for u64 {}
        impl Sealed for usize {}
    }

    /// A trait describing the representation of an automaton's state identifier.
    ///
    /// The purpose of this trait is to safely express both the possible state
    /// identifier representations that can be used in an automaton and to convert
    /// between state identifier representations and types that can be used to
    /// efficiently index memory (such as `usize`).
    ///
    /// In general, one should not need to implement this trait explicitly. Indeed,
    /// for now, this trait is sealed such that it cannot be implemented by any
    /// other type. In particular, this crate provides implementations for `u8`,
    /// `u16`, `u32`, `u64` and `usize`. (`u32` and `u64` are only provided for
    /// targets that can represent all corresponding values in a `usize`.)
    ///
    /// # Safety
    ///
    /// This trait is unsafe because the correctness of its implementations may be
    /// relied upon by other unsafe code. For example, one possible way to
    /// implement this trait incorrectly would be to return a maximum identifier
    /// in `max_id` that is greater than the real maximum identifier. This will
    /// likely result in wrap-on-overflow semantics in release mode, which can in
    /// turn produce incorrect state identifiers. Those state identifiers may then
    /// in turn access out-of-bounds memory in an automaton's search routine, where
    /// bounds checks are explicitly elided for performance reasons.
    pub unsafe trait StateID:
        private::Sealed
        + Clone + Copy + Debug + Eq + Hash + PartialEq + PartialOrd + Ord
    {
        /// Convert from a `usize` to this implementation's representation.
        ///
        /// Implementors may assume that `n <= Self::max_id`. That is, implementors
        /// do not need to check whether `n` can fit inside this implementation's
        /// representation.
        fn from_usize(n: usize) -> Self;

        /// Convert this implementation's representation to a `usize`.
        ///
        /// Implementors must not return a `usize` value greater than
        /// `Self::max_id` and must not permit overflow when converting between the
        /// implementor's representation and `usize`. In general, the preferred
        /// way for implementors to achieve this is to simply not provide
        /// implementations of `StateID` that cannot fit into the target platform's
        /// `usize`.
        fn to_usize(self) -> usize;

        /// Return the maximum state identifier supported by this representation.
        ///
        /// Implementors must return a correct bound. Doing otherwise may result
        /// in memory unsafety.
        fn max_id() -> usize;
    }

    unsafe impl StateID for usize {
        #[inline]
        fn from_usize(n: usize) -> usize { n }

        #[inline]
        fn to_usize(self) -> usize { self }

        #[inline]
        fn max_id() -> usize { ::std::usize::MAX }
    }

    unsafe impl StateID for u8 {
        #[inline]
        fn from_usize(n: usize) -> u8 { n as u8 }

        #[inline]
        fn to_usize(self) -> usize { self as usize }

        #[inline]
        fn max_id() -> usize { ::std::u8::MAX as usize }
    }

    unsafe impl StateID for u16 {
        #[inline]
        fn from_usize(n: usize) -> u16 { n as u16 }

        #[inline]
        fn to_usize(self) -> usize { self as usize }

        #[inline]
        fn max_id() -> usize { ::std::u16::MAX as usize }
    }

    #[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
    unsafe impl StateID for u32 {
        #[inline]
        fn from_usize(n: usize) -> u32 { n as u32 }

        #[inline]
        fn to_usize(self) -> usize { self as usize }

        #[inline]
        fn max_id() -> usize { ::std::u32::MAX as usize }
    }

    #[cfg(target_pointer_width = "64")]
    unsafe impl StateID for u64 {
        #[inline]
        fn from_usize(n: usize) -> u64 { n as u64 }

        #[inline]
        fn to_usize(self) -> usize { self as usize }

        #[inline]
        fn max_id() -> usize { ::std::u64::MAX as usize }
    }

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