Struct Complement 

pub struct Complement {
    pub dropped_nodes: HashMap<u32, Node>,
    pub dropped_arcs: Vec<(u32, u32, Edge)>,
    pub dropped_fans: Vec<Fan>,
    pub contraction_choices: HashMap<(u32, u32), Edge>,
    pub original_parent: HashMap<u32, u32>,
    pub source_fingerprint: u64,
    pub original_extra_fields: HashMap<u32, HashMap<String, Value>>,
    pub arc_edges: HashMap<(u32, u32), Edge>,
    pub original_values: HashMap<u32, Option<FieldPresence>>,
    pub synthesized_nodes: HashSet<u32>,
    pub contracted_into: HashMap<u32, u32>,
}

The complement: data discarded by a forward projection, needed by the backward direction to restore the original source instance.

When a forward projection maps a source instance to a target view, some nodes, arcs, and structural decisions are lost. The complement records all of this so the backward direction can reconstruct the full source.

Fields

dropped_nodes: HashMap<u32, Node>

Nodes from the source that do not appear in the target view.

dropped_arcs: Vec<(u32, u32, Edge)>

Arcs from the source that do not appear in the target view.

dropped_fans: Vec<Fan>

Fans from the source whose parent or children were dropped.

contraction_choices: HashMap<(u32, u32), Edge>

Resolver decisions made during ancestor contraction.

original_parent: HashMap<u32, u32>

Original parent mapping before contraction.

source_fingerprint: u64

Fingerprint of the source schema at projection time, used by the backward direction to validate that the complement matches the lens’s source schema.

original_extra_fields: HashMap<u32, HashMap<String, Value>>

Pre-transform extra_fields for nodes that had field_transforms applied. Used by the backward direction to restore original field values.

arc_edges: HashMap<(u32, u32), Edge>

Exact edge used for every arc in the view, keyed by (parent_id, child_id). This makes the backward direction deterministic when the source schema has parallel edges between the same vertex pair, ensuring the cartesian lift is unique.

original_values: HashMap<u32, Option<FieldPresence>>

Pre-coercion node.value for nodes that had __value__ field transforms applied. Used by the backward direction to restore the original leaf value.

synthesized_nodes: HashSet<u32>

View node ids synthesized during forward evaluation by the nest-style expansion_path mechanism. These nodes exist in the view (to satisfy the target schema’s multi-hop path) but have no counterpart in the source instance. The backward direction drops them when reconstructing the source.

contracted_into: HashMap<u32, u32>

For each dropped node, the surviving node it contracted into (its nearest surviving ancestor). Populated by the restrict pipeline’s ancestor contraction; the fiber of a target node is its direct preimage together with every source node recorded here as contracted into it.

Implementations

impl Complement

pub fn empty() -> Self

Create an empty complement (no data discarded).

pub fn is_empty(&self) -> bool

Returns true if the complement discards no data (lossless transformation).

The source_fingerprint is provenance metadata rather than discarded data, so a lossless projection that still records a fingerprint counts as empty.

Trait Implementations

impl Clone for Complement

fn clone(&self) -> Complement

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Complement

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

Formats the value using the given formatter.

impl Default for Complement

fn default() -> Complement

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Complement

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Complement

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.