Struct SizeBound 

pub struct SizeBound {
    pub bytes: usize,
    pub bounded: bool,
    pub plain: bool,
}

What one walk of a schema can say about size.

Fields

bytes: usize

Bytes, given the starting offset the walk was handed.

bounded: bool

False once an unbounded String / WString / Sequence is reached — bytes is then a FLOOR, not a bound, and callers must not size a buffer from it.

plain: bool

No variable-length member anywhere, so the WIRE length is fixed: bytes is EXACT rather than an upper bound.

Nothing dispatches on this, by decision (issues 1369 and 1422). It is the walk’s exactness property, asserted as such by plain_struct_bound_is_exact here and by bound_holds_against_the_writer_for_every_generated_type over the whole generated corpus, and it is surfaced as crate::schema::Message::IS_PLAIN / is_loan_eligible so there is ONE definition of “fixed layout” for whoever finally needs one.

The earlier text here said phase-380 W5 “wires this to borrow_loaned_message / subscription_supports_in_place”. It does not: W5 shipped the definition and left the wiring to whoever owns those slots (docs/roadmap/archived/phase-380-serialized-size-bound.md:228-232), and issue 0814 step 5 is where the wiring now waits — deliberately, since 0814 measures the loan surface as a cost on three of four backends and the natural consumer of this predicate is Cyclone-with-iceoryx, which no target we ship can reach. Do not gate the in-place path on it: that path hands the callback raw CDR to deserialize, which needs no fixed layout, so the flag would only take it away from every type with a String.

It is NOT “POD-blit eligible”, and a second flag under that name in the codegen IR was deleted by issue 1422 for disagreeing with this one on bool, on nested all-float64 structs and on mixed alignment. Nor does it make the bound version-INDEPENDENT: XCDR2’s DHEADER is fixed-width, so a plain type stays plain while its bound still differs per encoding (Time measures 12 under XCDR1 and 16 under XCDR2).

Trait Implementations

impl Clone for SizeBound

fn clone(&self) -> SizeBound

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for SizeBound

impl Debug for SizeBound

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

Formats the value using the given formatter.

impl Eq for SizeBound

impl PartialEq for SizeBound

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for SizeBound