Struct Keys 

pub struct Keys { /* private fields */ }

The names one collection has interned, and the ids it gave them.

Why nothing is ever removed

An id is the row index the name sits at, which costs the table nothing at all: no second array from id to row, no free list, no generation counter. It holds only while the rows do not move, and Elements moves its last row into the hole when something is taken out, so a removal here would silently repoint every document that used the moved name.

Never removing is the right answer rather than a limitation being tolerated. A field name that no document uses any more costs its bytes once and two bytes of nothing in the row array, and the alternative is either an indirection on every lookup forever or a scan of the whole collection to find out whether a name is still wanted. The table is capped at KEYS_MAX names, so the worst case is bounded and small.

Implementations

impl Keys

pub fn new() -> Keys

An empty table that has not allocated anything yet.

pub fn with_capacity(n: usize) -> Keys

An empty table with room for n names already taken.

pub fn intern(&mut self, name: &[u8]) -> Option<u16>

The id of name, giving it one if it does not have one yet.

None means the table is full or the name is longer than a name may be, and in both cases the caller writes the document with its keys as bytes instead. That is always safe, because the interned flag is per container and not per collection, so a collection can hold both kinds at once and everything already written stays readable.

pub fn id(&self, name: &[u8]) -> Option<u16>

The id name already has, without giving it one.

This is the read path: a lookup by name against an interned document resolves the name here once and then searches the document by id.

pub fn name(&self, id: u16) -> Option<&[u8]>

The name behind an id.

pub fn len(&self) -> usize

How many names are interned.

pub fn is_empty(&self) -> bool

Whether nothing has been interned yet.

pub fn is_full(&self) -> bool

Whether the next new name would be refused.

pub fn iter(&self) -> impl Iterator<Item = (&[u8], u16)>

Every name and its id, in id order.

pub fn memory_bytes(&self) -> usize

What the table costs.

Trait Implementations

impl Clone for Keys

fn clone(&self) -> Keys

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Keys

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

Formats the value using the given formatter.

impl Default for Keys

fn default() -> Keys

Returns the “default value” for a type.