Crate linotype

A keyed sequence reprojector that can optionally pin its values.

This crate can act as list state reconciliator for data-driven GUIs.

More generally speaking, it can be used to manage item-associated state of a changing sequence.

Features

"std"

Avoids aborting the process if the drop implementation of a key or value inside a pinning OwnedProjection panics.

This is not a default feature, but it’s recommended to enable it while your crate isn’t no_std anyway, even in libraries.
(However, not that enabling or disabling the "std" feature in this dependency is a subtle but breaking behaviour change for libraries, even if they don’t expose that behaviour directly, due to it potentially affecting whether such panics can be handled elsewhere.)

This is legal because pinning only implies an attempt to drop a pinned instance before it can be freed¹ (also since if a Drop implementation panics, that instance is (in general) considered dropped²).

However, catch_unwind is only available in std.

¹ core::pin: Drop guarantee
² Drop::drop: Panics

Performance Focus

This implementation is optimised for relatively small entry counts, like instances of a GUI component in a mutable list generated from some input sequence.

(Current) Caveats

• OwnedProjection reprojections have quadratic time complexity over the number of items.

  This could largely be mitigated by remembering how many entries in stale already have None instead of a value pointer, counting from each end.

• Return types are improper.

  Even if the closure types can’t be fully specified for now, it should be possible to expose the compound iterators directly. This would give access to the DoubleEndedIterator, ExactSizeIterator and FusedIterator implementations where appropriate.

  Moving the dynamic call further inwards would likely also improve Pin<OwnedProjection>’s performance for at least some operations.

• Use-case coverage isn’t great.

  This is mainly due to me right now needing only a (very) limited subset of what this type could in theory support.

  The most significant omission right now is likely any way to index the collection directly, or to extract entries by value.

• The stored-key reference &K isn’t exposed in the output of ongoing reprojections, as this reference is too short-lived for the Iterator trait.

  This reference could be exposed (e.g. via a .next_keyed() -> Option<(T, &K, &'b V)> method) with better return types.

Visit the repository to file an issue or pull-request.

Structs

OwnedProjection

A lingering projection/keyed sequence reprojector.

Traits

PinningOwnedProjection

The value-pinning OwnedProjection API.