Struct TransformContext 

pub struct TransformContext<'a> {
    pub child_values: HashMap<String, Value>,
    pub instance: Option<(&'a WInstance, u32)>,
}

What a field transform’s expressions may read besides the node itself.

Two things live here. child_values binds the node’s children by edge name: scalars always, and structural children when the caller asked for them via collect_child_values. instance carries the instance and the node’s id, which is what makes the graph-traversal builtins resolvable: children("self"), edge("self", k), edge_count("self") and anchor("self") all need a current node to walk from, and without one they evaluate to null.

A caller that holds a node but no instance (an edit lens rewriting a node in isolation, say) builds this with TransformContext::detached and gets the extra_fields-only behaviour.

Fields

child_values: HashMap<String, Value>

The node’s immediate children, keyed by edge name.

instance: Option<(&'a WInstance, u32)>

The instance and the id of the node being transformed.

Implementations

impl<'a> TransformContext<'a>

pub fn detached() -> Self

A context with neither children nor an instance: expressions see only the node’s own extra_fields.

pub fn new( schema: Option<&Schema>, instance: &'a WInstance, node_id: u32, transforms: &[FieldTransform], ) -> Self

A context over instance at node_id, binding every child the expressions in transforms might read.

pub const fn from_child_values(child_values: HashMap<String, Value>) -> Self

A context carrying pre-collected child values and no instance.

pub const fn with_child_values( &self, child_values: HashMap<String, Value>, ) -> Self

The same context with the child bindings replaced.

pub fn eval( &self, expr: &Expr, env: &Env, config: &EvalConfig, ) -> Result<Literal, ExprError>

Evaluate expr, resolving graph-traversal builtins against the instance when one is present.

Errors

Returns whatever the evaluator reports.

Trait Implementations

impl<'a> Clone for TransformContext<'a>

fn clone(&self) -> TransformContext<'a>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Debug for TransformContext<'a>

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

Formats the value using the given formatter.

impl Default for TransformContext<'_>

fn default() -> Self

Returns the “default value” for a type.