Expand description


This is in a proof of concept state and also internally uses a lot of not yet battle-tested unsafe code so use it on your own risk meanwhile if you are good with unsafe rust i would appreciate a soundness review

Allows to do almost arbitrary type projections. In comparison to other crates that do similar things it is more generic, does not require procedural macros and also does not impose additional requirements on target struct, if target struct is located in external crate that crate does not have to explicitly add a support for such projection(pin projection is an exception here).

Although as of now this crate doesn’t support enums yet, but it will be added later.

Currently can do following type of projections
  • Destructuring projection (similar to usual let <pattern> but also supports deref pattern, and also works if struct implements Drop which is just not called).
    Note that due to limitations of declaration macros currently unmentioned fields will be leaked.
  • Reference(&, &mut) projection (similar to match ergonomics in let <pattern> but also supports deref pattern)
  • Pin projection
  • Cell projection
  • MaybeUninit projection
  • Atomic(from atomic crate) projection
  • Option projection (which works together with other kinds of projections)
  • RefCell guards projection
  • raw pointers projections (*const T, *mut T, NonNull<T>)

Also adds two types of projectable pointers:

  • generic::GenericPointer - makes it possible to write code that is generic over the reference type.
  • OwningRef - reference that semantically owns data (sometimes referred as &own T in various proposals). On nightly(with nightly feature) it allows you to make object safe traits that accept Self by value.

Where possible, projections can additionally project through a Deref (including dereference by value via DerefOwned).

Here is a general overview of what you can do, see project! macro for more usage details.

    struct Foo {
        a: Bar,
        b: Rc<Cell<Bar>>,
        c: Pin<Box<Bar>>,
        d: Atomic<Bar>,

    struct Bar(usize,PhantomPinned);
    // needed only for pin projections

    fn test(arg: &Foo) {
        let Foo {
            a: Bar (e, ..),
            b: *Bar{ 0: cell },
            c: *Bar (_, f) ,
            d: Bar(atomic, ..),
        } = arg);
        let _: &usize = e;
        let _: &Cell<usize> = cell;
        let _: Pin<& PhantomPinned> = f;
        let _: &Atomic<usize> = atomic;

        let _: &usize = project!(arg -> a -> 0);
        let _: &Cell<usize> = project!(arg -> b -> 0);
        let _: Pin<& PhantomPinned> = project!(arg -> c -> 1);
        let _: &Atomic<usize> = project!(arg -> d -> 0);

Also allows dependent crates to define their own projections via traits. see atomic module for example of how to do a projection of a transparent field wrapper or Pin for doing projections on a custom reference type

MSRV: 1.54
License: MIT


pub use pin::*;


Pin projection support


Version of pin_projectable to work as derive macro with macro_rules_attribute
macro to create GenericPointer from regular references/pointers
Macro to delegate to PinDrop.
Macro to do all kinds of projections


Keeps track of stuff that was left of T when we moved out T::Target from it.
Marker type for the projections used in this crate. You can use that if you need to reuse existing projections.


Trait to, if necessary, transparently wrap type to prevent conflicting implementations
Version of Deref trait that allows moving out Self::Target from Self by value.
Implement it if your projection can meaningfully project through a deref operation
Implement that if you need to do some kind of post processing like unwrap something or panic if some soundness requirements are not satisfied
Trait to get raw pointer to underlying struct
Trait to wrap raw pointer to a field with a type that corresponds to a projection being done.
Implement this only if your projection can work with #[repr(packed)] structs.