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use {
    crate::{
        Context,
        Readable,
        Reader,
        Writable,
        Writer
    },
    hashbrown::HashMap,
};
use std::hash::{Hash, BuildHasher};
use crate::private::write_length;
use std::mem;

impl< 'a, C, K, V, S > Readable< 'a, C > for HashMap< K, V, S >
    where C: Context,
          K: Readable< 'a, C > + Eq + Hash,
          V: Readable< 'a, C >,
          S: BuildHasher + Default
{
    #[inline]
    fn read_from< R: Reader< 'a, C > >( reader: &mut R ) -> Result< Self, C::Error > {
        let length = crate::private::read_length( reader )?;
        reader.read_collection( length )
    }

    #[inline]
    fn minimum_bytes_needed() -> usize {
        4
    }
}

impl< C, K, V, S > Writable< C > for HashMap< K, V, S >
    where C: Context,
          K: Writable< C >,
          V: Writable< C >
{
    #[inline]
    fn write_to< W: ?Sized + Writer< C > >( &self, writer: &mut W ) -> Result< (), C::Error > {
        write_length( self.len(), writer )?;
        writer.write_collection( self.iter() )
    }

    #[inline]
    fn bytes_needed( &self ) -> Result< usize, C::Error > {
        unsafe_is_length!( self.len() );

        let mut count = mem::size_of::< u32 >();
        for (key, value) in self {
            count += key.bytes_needed()? + value.bytes_needed()?;
        }

        Ok( count )
    }
}