Enum FilterStrategy 

#[non_exhaustive]
pub enum FilterStrategy {
    PreFilter,
    PostFilter,
    InFilter,
    Auto,
}

How an index plans to apply a metadata Filter relative to its distance scan.

#[non_exhaustive] because selection logic will add variants (and likely adapter parameters) as approximate indexes start honouring filters. Callers should not exhaustively match on this enum and should not rely on the variant set being closed.

Variants in plain terms

• FilterStrategy::PreFilter — apply the predicate before the distance computation; only matching candidates enter the scan. Cheap when the predicate is selective, wasteful when it is broad.
• FilterStrategy::PostFilter — run the distance scan over every candidate, then drop hits that fail the predicate. Cheap when the predicate is broad, defeats top-k truncation when the predicate is selective (you may have to scan far past k to refill the result set).
• FilterStrategy::InFilter — interleave predicate evaluation with the distance walk so a graph index can prune branches it knows can’t produce surviving candidates. Requires MetadataIndex co-design.
• FilterStrategy::Auto — let the index pick from the above based on estimated selectivity. Requires the selectivity machinery that doesn’t exist yet; documented here so future configs can name it.

Examples

use iqdb_filter::FilterStrategy;

let chosen = FilterStrategy::PreFilter;
// Callers do not branch on this yet; the enum is vocabulary for later.
assert_ne!(chosen, FilterStrategy::PostFilter);

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

PreFilter

Apply the predicate before the distance scan.

PostFilter

Apply the predicate after the distance scan.

InFilter

Interleave the predicate with a graph traversal.

Auto

Let the index pick the strategy based on estimated selectivity.

Trait Implementations

impl Clone for FilterStrategy

fn clone(&self) -> FilterStrategy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for FilterStrategy

impl Debug for FilterStrategy

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

Formats the value using the given formatter.

impl Eq for FilterStrategy

impl Hash for FilterStrategy

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for FilterStrategy

fn eq(&self, other: &FilterStrategy) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for FilterStrategy