Struct Sum

pub struct Sum {
    pub variants: &'static [Variant],
    pub reserved: &'static [Tag],
    pub on_reserved_tag: Option<Tag>,
    pub on_unknown_tag: Option<Tag>,
}

A sum type — a discriminated union of Variants.

reserved lists retired variant tags. Like Product::reserved, this is always a compile-time tag-reuse guard; whether the runtime decoder routes such tags to a fallback variant is controlled by on_reserved_tag.

on_reserved_tag and on_unknown_tag opt into runtime-lenient decode of variant tags. Unlike products’ allow_unknown_tags (which just skips an entry), sums can’t skip a discriminator — the value is the discriminator — so the tolerance is expressed as “route to a designated fallback variant, discarding the payload”:

• on_reserved_tag — when set, the wire tag of the unit variant that acts as the backward-compat fallback. The macro fills it in iff a variant in the source carries #[tagged(on_reserved)]. On decode, any wire tag in reserved is routed here (payload discarded).
• on_unknown_tag — same shape, but for forward-compat: a variant marked #[tagged(on_unknown)] catches any wire tag that’s neither in variants nor in reserved. More dangerous than on_reserved: silently swallows real corruption alongside future-version tags, so opt in only when the fallback variant is a safe semantic substitute for “anything I don’t recognize” (e.g. metadata-bearing InlineType-shaped types — definitely not BrilligOpcode-shaped ones, where an unknown discriminator means we can’t execute the program).

A single variant may carry both #[tagged(on_reserved)] and #[tagged(on_unknown)] when the user wants the unified-catch-all behavior; in that case both fields point at the same tag.

Fields

variants: &'static [Variant]

reserved: &'static [Tag]

on_reserved_tag: Option<Tag>

on_unknown_tag: Option<Tag>

Implementations

impl Sum

pub fn variant_for(self, variant_name: &str) -> Option<Variant>

Look up a variant’s metadata by its serde name.

pub fn is_reserved(self, tag: Tag) -> bool

Whether tag is in the sum’s reserved list (a retired variant tag).

Trait Implementations

impl Clone for Sum

fn clone(&self) -> Sum

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Sum

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

Formats the value using the given formatter.

impl Copy for Sum