3 unstable releases

Uses old Rust 2015

0.2.0 Oct 24, 2018
0.1.1 Dec 15, 2017
0.1.0 Nov 13, 2017

#1174 in Algorithms

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Used in 2 crates

MPL-2.0 license

255 lines


An optional value trait and some implementations.

This crate is part of the fera project.

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Licensed under Mozilla Public License 2.0. Contributions will be accepted under the same license.


An optional value trait and some implementations.

There are two main uses for this:

  1. To abstract over the representation of optional values in generic code (Optional trait);
  2. To represent optional value in a space efficient way (OptionalBool, OptionalMax, OptionalMin, etc).

Note that this is complementary to std::option::Option, not a replacement. The idea is to use std::option::Option interface by converting an Optional value to an std::option::Option value.

The optional crate is similar, but we think that this module is more generic, mainly because optional crate is not concerned with the use case 1.

This crate can be used through fera crate.


One can use OptionalMax<usize> to represent an optional usize where the None value is represented by usize::MAX.

use fera_optional::*;
use std::mem;

assert_eq!(mem::size_of::<usize>(), mem::size_of::<OptionalMax<usize>>());

// default
let y = OptionalMax::<usize>::default();
assert_eq!(None, y.into_option());

// from a value
let x = OptionalMax::from(10usize);
assert_eq!(Some(&10), x.to_option_ref());
assert_eq!(10, *x.to_option_ref().unwrap());

// from an optional value
let z = Some(10);
let w = OptionalMax::from(z);
assert_eq!(Some(10), w.into_option());

Using OptionalBool

use fera_optional::*;
use std::mem;

assert_eq!(1, mem::size_of::<OptionalBool>());

let mut x = OptionalBool::from(false);

// change the value
*x.to_option_mut().unwrap() = true;