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    use core::hash::BuildHasher;
    use core::hash::Hash;
    use core::hash::Hasher;

    #[cfg(not(feature = "std"))]
    extern crate alloc;
    #[cfg(feature = "std")]
    extern crate std as alloc;

    #[cfg(feature = "specialize")]
    use crate::BuildHasherExt;
    #[cfg(feature = "specialize")]
    use alloc::string::String;
    #[cfg(feature = "specialize")]
    use alloc::vec::Vec;

    /// Provides a way to get an optimized hasher for a given data type.
    /// Rather than using a Hasher generically which can hash any value, this provides a way to get a specialized hash
    /// for a specific type. So this may be faster for primitive types.
    /// # Example
    /// ```
    /// use std::hash::BuildHasher;
    /// use ahash::RandomState;
    /// use ahash::CallHasher;
    ///
    /// let hash_builder = RandomState::new();
    /// //...
    /// let value: u32 = 17;
    /// let hash = u32::get_hash(&value, &hash_builder);
    /// ```
    /// Note that the type used to invoke `get_hash` must be the same a the type of value passed.
    /// For example get a hasher specialized on `[u8]` can invoke:
    /// ```
    /// /// use std::hash::BuildHasher;
    /// # use ahash::RandomState;
    /// # use ahash::CallHasher;
    /// # let hash_builder = RandomState::new();
    /// let bytes: [u8; 4] = [1, 2, 3, 4];
    /// let hash = <[u8]>::get_hash(&bytes, &hash_builder);
    /// ```
    pub trait CallHasher {
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64;
    }

    #[cfg(not(feature = "specialize"))]
    impl<T> CallHasher for T
    where
        T: Hash + ?Sized,
    {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            let mut hasher = build_hasher.build_hasher();
            value.hash(&mut hasher);
            hasher.finish()
        }
    }

    #[cfg(feature = "specialize")]
    impl<T> CallHasher for T
    where
        T: Hash + ?Sized,
    {
        #[inline]
        default fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            let mut hasher = build_hasher.build_hasher();
            value.hash(&mut hasher);
            hasher.finish()
        }
    }

    macro_rules! call_hasher_impl {
        ($typ:ty) => {
            #[cfg(feature = "specialize")]
            impl CallHasher for $typ {
                #[inline]
                fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
                    build_hasher.hash_as_u64(value)
                }
            }
        };
    }
    call_hasher_impl!(u8);
    call_hasher_impl!(u16);
    call_hasher_impl!(u32);
    call_hasher_impl!(u64);
    call_hasher_impl!(i8);
    call_hasher_impl!(i16);
    call_hasher_impl!(i32);
    call_hasher_impl!(i64);

    #[cfg(feature = "specialize")]
    impl CallHasher for u128 {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_fixed_length(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for i128 {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_fixed_length(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for usize {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_fixed_length(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for isize {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_fixed_length(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for [u8] {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_str(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for Vec<u8> {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_str(value)
        }
    }

    #[cfg(feature = "specialize")]
    impl CallHasher for str {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_str(value)
        }
    }

    #[cfg(all(feature = "specialize"))]
    impl CallHasher for String {
        #[inline]
        fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
            build_hasher.hash_as_str(value)
        }
    }

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

        #[test]
        #[cfg(feature = "specialize")]
        pub fn test_specialized_invoked() {
            let build_hasher = RandomState::with_seeds(1, 2, 3, 4);
            let shortened = u64::get_hash(&0, &build_hasher);
            let mut hasher = AHasher::new_with_keys(1, 2);
            0_u64.hash(&mut hasher);
            assert_ne!(hasher.finish(), shortened);
        }

        /// Tests that some non-trivial transformation takes place.
        #[test]
        pub fn test_input_processed() {
            let build_hasher = RandomState::with_seeds(2, 2, 2, 2);
            assert_ne!(0, u64::get_hash(&0, &build_hasher));
            assert_ne!(1, u64::get_hash(&0, &build_hasher));
            assert_ne!(2, u64::get_hash(&0, &build_hasher));
            assert_ne!(3, u64::get_hash(&0, &build_hasher));
            assert_ne!(4, u64::get_hash(&0, &build_hasher));
            assert_ne!(5, u64::get_hash(&0, &build_hasher));

            assert_ne!(0, u64::get_hash(&1, &build_hasher));
            assert_ne!(1, u64::get_hash(&1, &build_hasher));
            assert_ne!(2, u64::get_hash(&1, &build_hasher));
            assert_ne!(3, u64::get_hash(&1, &build_hasher));
            assert_ne!(4, u64::get_hash(&1, &build_hasher));
            assert_ne!(5, u64::get_hash(&1, &build_hasher));

            let xored = u64::get_hash(&0, &build_hasher) ^ u64::get_hash(&1, &build_hasher);
            assert_ne!(0, xored);
            assert_ne!(1, xored);
            assert_ne!(2, xored);
            assert_ne!(3, xored);
            assert_ne!(4, xored);
            assert_ne!(5, xored);
        }

        #[test]
        pub fn test_ref_independent() {
            let build_hasher = RandomState::with_seeds(1, 2, 3, 4);
            assert_eq!(u8::get_hash(&&1, &build_hasher), u8::get_hash(&1, &build_hasher));
            assert_eq!(u16::get_hash(&&2, &build_hasher), u16::get_hash(&2, &build_hasher));
            assert_eq!(u32::get_hash(&&3, &build_hasher), u32::get_hash(&3, &build_hasher));
            assert_eq!(u64::get_hash(&&4, &build_hasher), u64::get_hash(&4, &build_hasher));
            assert_eq!(u128::get_hash(&&5, &build_hasher), u128::get_hash(&5, &build_hasher));
            assert_eq!(
                str::get_hash(&"test", &build_hasher),
                str::get_hash("test", &build_hasher)
            );
            assert_eq!(
                str::get_hash(&"test", &build_hasher),
                String::get_hash(&"test".to_string(), &build_hasher)
            );
            #[cfg(feature = "specialize")]
            assert_eq!(
                str::get_hash(&"test", &build_hasher),
                <[u8]>::get_hash("test".as_bytes(), &build_hasher)
            );

            let build_hasher = RandomState::with_seeds(10, 20, 30, 40);
            assert_eq!(u8::get_hash(&&&1, &build_hasher), u8::get_hash(&1, &build_hasher));
            assert_eq!(u16::get_hash(&&&2, &build_hasher), u16::get_hash(&2, &build_hasher));
            assert_eq!(u32::get_hash(&&&3, &build_hasher), u32::get_hash(&3, &build_hasher));
            assert_eq!(u64::get_hash(&&&4, &build_hasher), u64::get_hash(&4, &build_hasher));
            assert_eq!(u128::get_hash(&&&5, &build_hasher), u128::get_hash(&5, &build_hasher));
            assert_eq!(
                str::get_hash(&&"test", &build_hasher),
                str::get_hash("test", &build_hasher)
            );
            assert_eq!(
                str::get_hash(&&"test", &build_hasher),
                String::get_hash(&"test".to_string(), &build_hasher)
            );
            #[cfg(feature = "specialize")]
            assert_eq!(
                str::get_hash(&&"test", &build_hasher),
                <[u8]>::get_hash(&"test".to_string().into_bytes(), &build_hasher)
            );
        }
    }