Enum DuplicateKeyPolicy 

#[non_exhaustive]
pub enum DuplicateKeyPolicy {
    Error,
    FirstWins,
    LastWins,
    PassThrough,
}

Duplicate key handling policy for mappings.

Except with Self::PassThrough, YAML integer keys are compared by their parsed integer value, so 0xB and 11 are duplicates even when the target key type is String. The retained key preserves its original spelling when deserialized into a string. Merge expansion always uses YAML key identity.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Error

Error out on encountering a duplicate key.

FirstWins

First key wins: later duplicate pairs are skipped (key+value are consumed and ignored).

LastWins

Last key wins: retain the later value. Struct fields are buffered and collapsed before Serde sees them. Maps stream until an integer-containing key requires numeric comparison, then buffer the remaining entries to retain the last key’s original spelling and value.

PassThrough

Forward repeated explicit mapping entries to the receiving Serde visitor.

This matches serde_yaml’s visitor-driven handling of explicit entries: derived structs reject repeated fields, standard maps keep the last value, and custom visitors decide whether to reject, replace, or retain duplicates. Integer-equivalent keys such as 0xB and 11 are also forwarded separately.

Merge expansion still follows MergeKeyPolicy and suppresses overridden entries. Repeated keys within a merge source retain the first entry. Use MergeKeyPolicy::AsOrdinary to forward literal << entries as well.

This is a permissive extension: YAML requires unique mapping keys. Self::Error remains the default.

Trait Implementations

impl Clone for DuplicateKeyPolicy

fn clone(&self) -> DuplicateKeyPolicy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for DuplicateKeyPolicy

impl Debug for DuplicateKeyPolicy

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

Formats the value using the given formatter.