Struct StackCache

struct StackCache {
    items: [Item; 32],
    idx: [usize; 32],
}

A very small cache of searches of a borrow stack, mapping Items to their position in said stack.

It may seem like maintaining this cache is a waste for small stacks, but (a) iterating over small fixed-size arrays is super fast, and (b) empirically this helps a lot, probably because runtime is dominated by large stacks.

Fields

items: [Item; 32]

idx: [usize; 32]

Implementations

impl StackCache

fn add(&mut self, idx: usize, item: Item)

When a tag is used, we call this function to add or refresh it in the cache.

We use the position in the cache to represent how recently a tag was used; the first position is the most recently used tag. So an add shifts every element towards the end, and inserts the new element at the start. We lose the last element. This strategy is effective at keeping the most-accessed items in the cache, but it costs a linear shift across the entire cache when we add a new tag.

Trait Implementations

impl Clone for StackCache

fn clone(&self) -> StackCache

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for StackCache

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 512 bytes