Enum TermAssignment 

pub enum TermAssignment {
    Compute {
        target: String,
        scope: TermScope,
        term: Expr,
        inverse: Option<Expr>,
        coercion_class: CoercionClass,
    },
    Rename {
        old: String,
        new: String,
    },
    Drop {
        key: String,
    },
    Default {
        key: String,
        value: Value,
    },
    Keep {
        keys: Vec<String>,
    },
    MapReferences {
        field: String,
        rename_map: HashMap<String, Option<String>>,
    },
    AtPath {
        path: Vec<String>,
        inner: Box<Self>,
    },
    Case {
        branches: Vec<TermBranch>,
    },
}

An op-to-term assignment: how one migrated field is produced from a source row.

A Self::Compute assignment carries a term (panproto_expr::Expr) whose free variables are source field names; evaluating it substitutes the row’s field values for those variables. This is the substitution semantics through which the migration functors act on values: Delta (crate::functor::functor_restrict) and Sigma (wtype_extend, crate::functor::functor_extend) compute migrated columns by substituting each surviving row. The remaining variants describe structural field operations (rename, drop, keep, default, reference remap, nested-path scoping, and case analysis).

Every FieldTransform variant translates to a TermAssignment via Self::from_field_transform and lowers back via Self::to_field_transform; applying a translated assignment produces the same result as applying the original transform. Migrations produced by panproto-mig’s compiler carry their value transforms as term assignments rather than direct FieldTransforms.

Variants

Compute

Compute target by substituting the row’s values into term.

Fields

target: String

The migrated field written by this assignment.

scope: TermScope

Which source fields the term sees.

term: Expr

The term computing the field.

inverse: Option<Expr>

Optional inverse for round-tripping.

coercion_class: CoercionClass

Round-trip classification of this assignment.

Rename

Rename field old to new.

Fields

old: String

The current field name.

new: String

The new field name.

Drop

Drop field key.

Fields

key: String

The field to remove.

Default

Add value at key when the field is absent.

Fields

key: String

The field to add.

value: Value

The default value.

Keep

Keep only the listed fields.

Fields

keys: Vec<String>

The fields to retain.

MapReferences

Remap string references in field through rename_map.

Fields

field: String

The field carrying references.

rename_map: HashMap<String, Option<String>>

Old-name to new-name map (None removes the reference).

AtPath

Apply inner at a nested path within the row’s Value tree.

Fields

path: Vec<String>

The path of nested object keys.

inner: Box<Self>

The assignment applied at the resolved path.

Case

First matching branch’s assignments apply.

Fields

branches: Vec<TermBranch>

Ordered branches; the first matching predicate wins.

Implementations

impl TermAssignment

pub fn from_field_transform(ft: &FieldTransform) -> Self

Translate a FieldTransform into the equivalent term assignment.

pub fn to_field_transform(&self) -> FieldTransform

Lower this term assignment to the equivalent FieldTransform.

pub fn coercion_class(&self) -> CoercionClass

Round-trip classification of this assignment, matching the classification of its lowered FieldTransform.

Trait Implementations

impl Clone for TermAssignment

fn clone(&self) -> TermAssignment

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for TermAssignment

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for TermAssignment

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for TermAssignment

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

where __S: Serializer,

Serialize this value into the given Serde serializer.