You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: hashes.rs
    path of file: ./repos/vonuvoli-scheme/sources
    
    the code of the file until where you have to start completion: 

use super::constants::exports::*;
use super::contexts::exports::*;
use super::errors::exports::*;
use super::values::exports::*;

#[ cfg ( feature = "vonuvoli_expressions" ) ]
#[ cfg ( feature = "vonuvoli_values_lambda" ) ]
use super::lambdas::exports::*;

use super::prelude::*;




pub mod expor
    
pub fn hash_value_with_blake2b <Value : HashValue, ValueRef : StdAsRef<Value>> (value : ValueRef, bits : usize, key : Option<&[u8]>, mode : HashMode) -> (Outcome<StdBox<[u8]>>) {
	let size = bits / 8;
	let key = key.unwrap_or (&[]);
	if (size * 8) != bits {
		fail! (0x355ed665);
	}
	if size == 0 {
		fail! (0x958adc76);
	}
	if size > 64 {
		fail! (0x176342ac);
	}
	if key.len () > 64 {
		fail! (0x4be93a98);
	}
	use ext::digest::VariableOutput as _;
	use ext::digest::Update as _;
	let mut hasher = {
		// NOTE:  let mut hasher = ext::blake2::Blake2bVar::with_key (size, key);
		let mut hasher = try_or_fail! (ext::blake2::Blake2bVar::new (size), 0xa9d2d900);
		*(unsafe { mem::transmute::<_, &mut ext::blake2::Blake2bVarCore> (&mut hasher) }) = ext::blake2::Blake2bVarCore::new_with_params (&[], &[], key.len (), size);
		hasher.update (key);
		hasher
	};
	r#try! (hash_value_with_writer (value, &mut hasher, mode));
	let mut hash = StdVec::new ();
	hash.resize_with (size, Default::default);
	try_or_fail! (hasher.finalize_variable (&mut hash), 0x55741ef5);
	let hash = hash.into_boxed_slice ();
	succeed! (hash);
}