Enum EncodingStrategy

pub enum EncodingStrategy {
    Tagged,
    Array,
}

On-wire shape for product types (structs, tuple structs, enum-variant payloads). Picked per-type on the Serializer (see Serializer::new / Serializer::with_strategy). Enum variants are always int-keyed under MsgpackTagged regardless of strategy — the strategy only affects struct shape.

• EncodingStrategy::Tagged (default) — int-keyed fixmap {0: a, 1: b, …}. Schema-evolution friendly: identification is by tag, so fields can be added, removed (via #[tagged(reserved(...))]), or reordered freely. Costs one byte per field for the tag.
• EncodingStrategy::Array — positional fixarray [a, b, …], fields emitted in tag-ascending order. Minimum overhead. Identification is by position, so evolvability is limited to trailing changes:
  • Adding a trailing field is backward-compat when the field is marked #[serde(default)] — V1 wire (shorter) decodes into V2 type, the default fills the new position.
  • Removing a trailing field is forward-compat when the type opts into #[tagged(allow_unknown_tags)] — V2 wire (longer) decodes into V1 type, the extra trailing position is ignored.
  • Anything else (middle insert/remove, reorder, type change) is wire-breaking. Pick this strategy for small leaf types where size wins over flexibility and the type is unlikely to need middle-of-shape edits.

Auto-downgrade to Tagged. If a type has #[tagged(reserved(N))] where N falls between (or before) the active tags, requesting Array for it would corrupt round-trips: V2’s positional wire only carries active values, but the decoder walks a merged-sorted layout of (active + reserved) tags and would drain a wire byte at the reserved slot intended for a later active field. The encoder detects this and silently switches to Tagged for that product only — other types in the same serializer keep their configured strategy. Strictly-trailing reserved tags (every reserved tag greater than every active tag) keep Array: the decoder hits wire_remaining == 0 before reaching the trailing reserved slot, so positional alignment holds. The migration guide in the crate README walks through both cases with examples.

The decoder probes the wire shape (fixmap vs. fixarray) per struct at decode time, so a single buffer can mix both strategies across nested types freely.

Variants

Tagged

Int-keyed map. Default — most backward/forward compatible.

Array

Positional array. Smaller; not schema-evolvable.

Trait Implementations

impl Clone for EncodingStrategy

fn clone(&self) -> EncodingStrategy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for EncodingStrategy

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

Formats the value using the given formatter.

impl Default for EncodingStrategy

fn default() -> EncodingStrategy

Returns the “default value” for a type.

impl PartialEq for EncodingStrategy

fn eq(&self, other: &EncodingStrategy) -> 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 Copy for EncodingStrategy

impl Eq for EncodingStrategy

impl StructuralPartialEq for EncodingStrategy