Crate yoke

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Expand description

This crate provides Yoke<Y, C>, which allows one to “yoke” (attach) a zero-copy deserialized object (say, a Cow<'a, str>) to the source it was deserialized from, (say, an Rc<[u8]>), known in this crate as a “cart”, producing a type that looks like Yoke<Cow<'static, str>, Rc<[u8]>> and can be moved around with impunity.

Succinctly, this allows one to “erase” static lifetimes and turn them into dynamic ones, similarly to how dyn allows one to “erase” static types and turn them into dynamic ones.

Most of the time the yokeable Y type will be some kind of zero-copy deserializable abstraction, potentially with an owned variant (like Cow, ZeroVec, or an aggregate containing such types), and the cart C will be some smart pointer like Box<T>, Rc<T>, or Arc<T>, potentially wrapped in an Option<T>.

The key behind this crate is Yoke::get(), where calling .get() on a type like Yoke<Cow<'static, str>, _> will get you a short-lived &'a Cow<'a, str>, restricted to the lifetime of the borrow used during .get(). This is entirely safe since the Cow borrows from the cart type C, which cannot be interfered with as long as the Yoke is borrowed by .get(). .get() protects access by essentially reifying the erased lifetime to a safe local one when necessary.

See the documentation of Yoke for more details.


Types to enable polymorphic carts.
This module contains helper types for erasing Cart types.
Workarounds for adding trait bounds to yoke objects.


A Cow-like borrowed object “yoked” to its backing data.


This trait marks cart types that do not change source on cloning
A type implementing IsCovariant<'a> is covariant with respect to lifetime 'a.
The Yokeable<'a> trait is implemented on the 'static version of any zero-copy type; for example, Cow<'static, T> implements Yokeable<'a> (for all 'a). One can use Yokeable::Output on this trait to obtain the “lifetime’d” value of the Cow<'static, T>, e.g. <Cow<'static, T> as Yokeable<'a>'>::Output is Cow<'a, T>.

Derive Macros

Custom derive for yoke::Yokeable,