% containerof - Macros supporting intrusive data structures in Rust.

An intrusive structure is a general-purpose structure directly embedded within a containing structure, in order to add that general-purpose facility to the container. As an example, one might use an intrusive "link" structure to allow objects to be organized in a linked-list:

# #[macro_use]
extern crate containerof;
struct Link {
    next: Option<ContainerLink>,
}
struct List {
    head: Option<ContainerLink>,
    tail: Option<ContainerLink>,
}

struct Container {
    link: Link,
}
containerof_intrusive!(ContainerLink = Container:link::Link);
# fn main() {}

While this module does not provide a linked-list implementation (for separation-of-concerns reasons, I believe a linked-list implementation belongs in a separate crate), it does provide some necessary abstractions for using intrusive structures:

• The containerof_field_offset! macro, which identifies the location of a field in a containing structure. This isn't too useful in itself, but is necessary to support:
• The containerof_intrusive! macro, which provides a newtype that describes the translation between the "intrusive" field and the "container" structure.

Usage

Here is an example implementation of Church-numerals using an intrusive linked-list:

#[macro_use]
extern crate containerof;
use containerof::*;

struct Church {
    next: Option<ChurchLink>,
}

containerof_intrusive!(ChurchLink = Church:next::Option<ChurchLink>);

impl Church {
    fn new() -> OwnBox<Church> {
        unsafe { OwnBox::from_box(Box::new(Church { next: None })) }
    }
    fn push(next: OwnBox<Church>) -> OwnBox<Church> {
        unsafe { OwnBox::from_box(Box::new(Church { next: Some(Intrusive::from_container(next)) })) }
    }
    fn pop(me: OwnBox<Church>) -> Option<OwnBox<Church>> {
        let me = unsafe { me.into_box() };
        match me.next {
            None => None,
            Some(x) => Some(unsafe { x.into_container() }),
        }
    }
}
# fn main() {}

Concepts

containerof uses three main concepts for working with intrusive structures:

1. The intrusive structure itself (Church.next in the above example);
2. The containing structure (Church);
3. The translation type, for getting a container from a field, or vice-versa (ChurchLink).

In addition, there are three auxiliary structures for managing ownership and borrowing of intrusive structures:

1. OwnBox, which is a pointer type representing ownership of the container (even if all you have is a field reference).
2. BorrowBox, which is a pointer type representing a borrow of the container.
3. BorrowBoxMut, which is a pointer type representing a mutable borrow of the container.

Contributing

1. Fork it ( https://github.com/aidancully/containerof/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request