Optional

This package aims to offer some Option<_>-like values that allow a space-optimized representation.

As of now there is a type OptionBool. It works very much like an Option<bool> (and indeed mostly copies its interface). There are only a few additional methods where Option<bool> would recieve or return another Option<bool>, a _bool prefix is used to receive/return OptionBool instead.

Note that due to the internal conversion it is generally impossible to create iter_mut() or as_mut_slice() methods. Therefore those methods cannot be supported.

Not only does OptionBool improve space efficiency as opposed to Option<bool>, most methods also perform a little faster in my benchmarks. On nightly, On an Intel(R) Core(TM)2 Quad CPU Q8400 @ 2.66GHz running LUbuntu 15.04 with a 3.19.0-23-generic kernel and Rust 1.8.0-nightly as of 2016-01-22, I get the following results:

test bench_and_bool_opt        ... bench:       1,490 ns/iter (+/- 38)
test bench_and_opt             ... bench:       1,667 ns/iter (+/- 37)
test bench_and_std             ... bench:       1,695 ns/iter (+/- 30)
test bench_as_slice_iter_opt   ... bench:       2,211 ns/iter (+/- 16)
test bench_as_slice_opt        ... bench:       1,507 ns/iter (+/- 23)
test bench_from_opt            ... bench:       1,795 ns/iter (+/- 137)
test bench_is_some_opt         ... bench:       1,443 ns/iter (+/- 17)
test bench_is_some_std         ... bench:       1,659 ns/iter (+/- 17)
test bench_iter_opt            ... bench:       2,212 ns/iter (+/- 39)
test bench_iter_std            ... bench:       1,553 ns/iter (+/- 22)
test bench_map_invert_opt      ... bench:       2,918 ns/iter (+/- 35)
test bench_map_invert_opt_bool ... bench:       2,063 ns/iter (+/- 23)
test bench_map_invert_std      ... bench:       2,510 ns/iter (+/- 36)
test bench_map_or_else_opt     ... bench:       2,268 ns/iter (+/- 35)
test bench_map_or_else_std     ... bench:       2,309 ns/iter (+/- 33)
test bench_map_or_opt          ... bench:       1,669 ns/iter (+/- 19)
test bench_map_or_std          ... bench:       1,975 ns/iter (+/- 26)
test bench_or_bool_opt         ... bench:       1,424 ns/iter (+/- 33)
test bench_or_else_bool_opt    ... bench:       1,654 ns/iter (+/- 30)
test bench_or_else_opt         ... bench:       1,766 ns/iter (+/- 24)
test bench_or_else_std         ... bench:       1,529 ns/iter (+/- 13)
test bench_or_opt              ... bench:       1,806 ns/iter (+/- 50)
test bench_or_std              ... bench:       1,729 ns/iter (+/- 28)
test bench_to_opt              ... bench:       1,979 ns/iter (+/- 87)
test bench_unwrap_opt          ... bench:       1,700 ns/iter (+/- 29)
test bench_unwrap_or_else_opt  ... bench:       1,666 ns/iter (+/- 19)
test bench_unwrap_or_else_std  ... bench:       2,149 ns/iter (+/- 31)
test bench_unwrap_or_opt       ... bench:       1,653 ns/iter (+/- 23)
test bench_unwrap_or_std       ... bench:       2,124 ns/iter (+/- 30)
test bench_unwrap_std          ... bench:       1,645 ns/iter (+/- 20)

[...]

test bench_as_slice_iter_opt_f32 ... bench:       2,090 ns/iter (+/- 35)
test bench_as_slice_iter_opt_f64 ... bench:       1,870 ns/iter (+/- 33)
test bench_as_slice_iter_opt_i16 ... bench:       1,937 ns/iter (+/- 24)
test bench_as_slice_iter_opt_i32 ... bench:       2,028 ns/iter (+/- 47)
test bench_as_slice_iter_opt_i64 ... bench:       1,680 ns/iter (+/- 32)
test bench_as_slice_iter_opt_i8  ... bench:       2,032 ns/iter (+/- 16)
test bench_as_slice_iter_opt_u16 ... bench:       1,937 ns/iter (+/- 28)
test bench_as_slice_iter_opt_u32 ... bench:       2,030 ns/iter (+/- 59)
test bench_as_slice_iter_opt_u64 ... bench:       1,775 ns/iter (+/- 135)
test bench_as_slice_iter_opt_u8  ... bench:       2,031 ns/iter (+/- 23)
test bench_is_some_opt_f32       ... bench:       1,721 ns/iter (+/- 17)
test bench_is_some_opt_f64       ... bench:       1,721 ns/iter (+/- 24)
test bench_is_some_opt_u16       ... bench:       1,711 ns/iter (+/- 26)
test bench_is_some_opt_u32       ... bench:       1,677 ns/iter (+/- 25)
test bench_is_some_opt_u64       ... bench:       1,664 ns/iter (+/- 31)
test bench_is_some_opt_u8        ... bench:       1,724 ns/iter (+/- 22)
test bench_is_some_std_f32       ... bench:       1,466 ns/iter (+/- 22)
test bench_is_some_std_f64       ... bench:       1,465 ns/iter (+/- 18)
test bench_is_some_std_u16       ... bench:       1,470 ns/iter (+/- 29)
test bench_is_some_std_u32       ... bench:       1,465 ns/iter (+/- 18)
test bench_is_some_std_u64       ... bench:       1,474 ns/iter (+/- 61)
test bench_is_some_std_u8        ... bench:       1,850 ns/iter (+/- 35)
test bench_iter_opt_f32          ... bench:       1,828 ns/iter (+/- 17)
test bench_iter_opt_f64          ... bench:       1,845 ns/iter (+/- 25)
test bench_iter_opt_i16          ... bench:       1,755 ns/iter (+/- 17)
test bench_iter_opt_i32          ... bench:       1,755 ns/iter (+/- 18)
test bench_iter_opt_i64          ... bench:       1,547 ns/iter (+/- 43)
test bench_iter_opt_i8           ... bench:       1,754 ns/iter (+/- 17)
test bench_iter_opt_u16          ... bench:       1,754 ns/iter (+/- 21)
test bench_iter_opt_u32          ... bench:       1,563 ns/iter (+/- 16)
test bench_iter_opt_u64          ... bench:       1,534 ns/iter (+/- 20)
test bench_iter_opt_u8           ... bench:       1,754 ns/iter (+/- 18)
test bench_iter_std_f32          ... bench:       1,563 ns/iter (+/- 39)
test bench_iter_std_f64          ... bench:       1,587 ns/iter (+/- 17)
test bench_iter_std_i16          ... bench:       1,487 ns/iter (+/- 32)
test bench_iter_std_i32          ... bench:       1,587 ns/iter (+/- 20)
test bench_iter_std_i64          ... bench:       1,587 ns/iter (+/- 25)
test bench_iter_std_i8           ... bench:       1,631 ns/iter (+/- 98)
test bench_iter_std_u16          ... bench:       1,488 ns/iter (+/- 23)
test bench_iter_std_u32          ... bench:       1,590 ns/iter (+/- 59)
test bench_iter_std_u64          ... bench:       1,587 ns/iter (+/- 25)
test bench_iter_std_u8           ... bench:       1,623 ns/iter (+/- 72)
test bench_map_opt_f32           ... bench:       1,959 ns/iter (+/- 67)
test bench_map_opt_f64           ... bench:       1,654 ns/iter (+/- 40)
test bench_map_opt_u16           ... bench:       1,789 ns/iter (+/- 31)
test bench_map_opt_u32           ... bench:       2,431 ns/iter (+/- 43)
test bench_map_opt_u64           ... bench:       1,432 ns/iter (+/- 32)
test bench_map_opt_u8            ... bench:       1,813 ns/iter (+/- 18)
test bench_map_or_opt_f32        ... bench:       1,623 ns/iter (+/- 17)
test bench_map_or_opt_f64        ... bench:       1,669 ns/iter (+/- 22)
test bench_map_or_opt_u16        ... bench:       1,717 ns/iter (+/- 18)
test bench_map_or_opt_u32        ... bench:       1,640 ns/iter (+/- 19)
test bench_map_or_opt_u64        ... bench:       1,579 ns/iter (+/- 40)
test bench_map_or_opt_u8         ... bench:       1,814 ns/iter (+/- 20)
test bench_map_or_std_f32        ... bench:       1,537 ns/iter (+/- 28)
test bench_map_or_std_f64        ... bench:       1,777 ns/iter (+/- 28)
test bench_map_or_std_u16        ... bench:       1,931 ns/iter (+/- 37)
test bench_map_or_std_u32        ... bench:       1,807 ns/iter (+/- 22)
test bench_map_or_std_u64        ... bench:       1,786 ns/iter (+/- 15)
test bench_map_or_std_u8         ... bench:       2,010 ns/iter (+/- 19)
test bench_map_std_f32           ... bench:       1,811 ns/iter (+/- 37)
test bench_map_std_f64           ... bench:       1,925 ns/iter (+/- 45)
test bench_map_std_u16           ... bench:       2,357 ns/iter (+/- 23)
test bench_map_std_u32           ... bench:       2,262 ns/iter (+/- 102)
test bench_map_std_u64           ... bench:       1,933 ns/iter (+/- 48)
test bench_map_std_u8            ... bench:       2,545 ns/iter (+/- 65)

Apart from OptionBool, there is a struct Optioned<T> that is similar to Option but needs no additional storage, declaring a None value instead. Their are impls For i8..64, u8..64, isize, usize, f32 and f64, and it's easy enough to Implement it for your own type (have a look at the Noned trait). The None value for the int types is their MIN, for the unsigned types is their MAX and for floats is NAN (regardless of sign).

Documentation

API documentation

You also may want to have a look at the very well documented Option type, on which this crate is based.

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.