Struct CopyOnWriteMutation 

pub struct CopyOnWriteMutation {
    pub express_id: u32,
    pub index: usize,
    pub value: String,
    pub referrer_id: u32,
    pub referrer_index: usize,
}

Replace one attribute of a record that other records share, by copying the record and repointing a single referrer at the copy.

The reason this is a writer job rather than a caller one is the id. A copy needs a number no record holds, and the writer is what knows max_id; a caller that allocates its own has to agree with PropMutation’s synthesis about which numbers are free, and two allocators sharing one space is a collision waiting for the first export that uses both.

Doing it here also keeps the copy inside the emit path, so it is counted in StepStats::written and converted when the export targets another schema. A record spliced into the output afterwards is neither.

Property sets are the case this exists for. IFC exporters routinely give each element its own IfcPropertySet and point them all at one IfcPropertySingleValue per distinct value, so editing that value in place changes it for every element sharing it. Copying first changes one.

Fields

express_id: u32

The record to copy.

index: usize

Which attribute of the copy to replace, zero-based.

value: String

The replacement, STEP-serialized, e.g. IFCLABEL('2HR').

referrer_id: u32

The record that should point at the copy instead of the original.

referrer_index: usize

Which attribute of the referrer holds that reference. A list attribute is rewritten with the one reference substituted and the rest untouched.

Trait Implementations

impl Clone for CopyOnWriteMutation

fn clone(&self) -> CopyOnWriteMutation

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for CopyOnWriteMutation

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

Formats the value using the given formatter.

impl PartialEq for CopyOnWriteMutation

fn eq(&self, other: &CopyOnWriteMutation) -> 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 Eq for CopyOnWriteMutation

impl StructuralPartialEq for CopyOnWriteMutation