empty-option: guards for safely taking and dealing with values from mutable references to Option<T>

This crate provides convenient wrappers for dealing with &mut Option<T>. There are two main types, OptionGuard and OptionGuardMut:

OptionGuard

Using EmptyOptionExt::steal on an &mut Option<T> produces the T from the option as well as an OptionGuard. If OptionGuard::restore is not called before the OptionGuard is dropped, then a panic will occur.

Examples

Calling guard.restore() puts the stolen value back into the original option:

use empty_option::EmptyOptionExt;

// A mutable option, from which we shall steal a value!
let mut thing = Some(5);

// Scope so that when we do `guard.restore()`, the mutable borrow on `thing` will end.
{
    // Steal the value - we now have the guard and also a concrete `T` from our `Option<T>`.
    let (guard, five) = thing.steal();

    assert_eq!(five, 5);

    // Move the value back into `thing` - we're done.
    guard.restore(6);
}

// The value is returned by `guard.restore()`.
assert_eq!(thing, Some(6));

But, if the guard is dropped instead, a runtime panic results.

use empty_option::EmptyOptionExt;

let mut thing = Some(5);

let (_, _) = thing.steal();

// Never return the value!

Calling .steal() on a None immediately panics:

let mut thing = None;

// Panics here!
let (guard, _) = thing.steal();

guard.restore(5);

OptionGuardMut

Using EmptyOptionExt::steal_mut on an &mut Option<T> produces an OptionGuardMut, which dereferences to a T. To get the inner value out, OptionGuardMut::into_inner can be called. On Drop, if the OptionGuardMut is not consumed with OptionGuardMut::into_inner, the value in the OptionGuardMut will be returned to the Option that it was borrowed from.

Examples

Take a value from an option, which is automatically returned:

use empty_option::EmptyOptionExt;

let mut thing = Some(5);

{
    let mut stolen = thing.steal_mut();

    assert_eq!(*stolen, 5);

    *stolen = 6;
}

assert_eq!(thing, Some(6));

If the guard is consumed, the value is never returned.

use empty_option::EmptyOptionExt;

let mut thing = Some(5);

{
    // Keep the thing!
    let stolen = thing.steal_mut().into_inner();

    assert_eq!(stolen, 5);
}

assert_eq!(thing, None);

Calling steal_mut on a None immediately panics:

let mut thing: Option<i32> = None;

// Panics here!
thing.steal_mut();

License

Licensed under either of

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