Struct MapView 

pub struct MapView<'a, K, V> { /* private fields */ }

A borrowed view of a map field.

Protobuf map<K, V> fields are encoded as repeated sub-messages, each containing a key (field 1) and value (field 2). This type stores the decoded entries in a Vec<(K, V)>, borrowing string and bytes keys/values directly from the input buffer.

Lookup is O(n) linear scan, which is appropriate for the typically small maps found in protobuf messages (metadata labels, headers, etc.). If duplicate keys appear on the wire, get returns the last occurrence (last-write-wins, per the protobuf spec).

For larger maps where O(1) lookup matters, collect into a HashMap:

use std::collections::HashMap;
let index: HashMap<&str, &str> = view.labels.into_iter().collect();

Duplicate keys resolve last-write-wins in the collected map (matching proto map semantics), since HashMap::from_iter keeps the last value.

Allocation

Like RepeatedView, the Vec backing store requires allocation. The individual keys and values borrow from the input buffer where possible (string keys as &'a str, bytes values as &'a [u8]).

Implementations

impl<'a, K, V> MapView<'a, K, V>

pub fn new(entries: Vec<(K, V)>) -> Self

Construct from a Vec of entries, for ViewEncode use.

Duplicate keys are kept and all encoded — valid protobuf wire data (decoders apply last-write-wins). Mirrors RepeatedView::new.

pub fn len(&self) -> usize

Returns the number of entries (including duplicates).

pub fn is_empty(&self) -> bool

Returns true if there are no entries.

pub fn iter(&self) -> Iter<'_, (K, V)>

Iterate over all entries in wire order.

If duplicate keys exist, all occurrences are yielded.

pub fn keys(&self) -> impl Iterator<Item = &K>

Iterate over all keys in wire order.

pub fn values(&self) -> impl Iterator<Item = &V>

Iterate over all values in wire order.

pub fn get<Q>(&self, key: &Q) -> Option<&V>

where K: Borrow<Q>, Q: PartialEq + ?Sized,

Look up a value by key, returning the last occurrence (last-write-wins).

Accepts any type that K can borrow as, so map.get("key") works when K is &str. O(n) scan.

pub fn contains_key<Q>(&self, key: &Q) -> bool

where K: Borrow<Q>, Q: PartialEq + ?Sized,

Returns true if an entry with the given key exists.

pub fn iter_unique(&self) -> impl Iterator<Item = &(K, V)>

where K: PartialEq,

Iterate over key-value pairs with duplicate keys removed.

Each distinct key is yielded exactly once, at the position of its last wire occurrence, carrying that occurrence’s value — i.e. last-write-wins, mirroring the merge semantics that an owned HashMap decode applies. Callers that need first-occurrence position should use iter and filter themselves.

Used by the generated view Serialize impl: a JSON object cannot hold duplicate keys, but MapView preserves all wire entries (including malformed duplicates), so the JSON encode path must deduplicate. The implementation is allocation-free and O(n²) — for each entry, scan the remaining entries for a later occurrence of the same key. Duplicate map keys are invalid per the protobuf encoding spec and only arise in adversarial or conformance-test wire data, so n is effectively always small.

pub fn len_unique(&self) -> usize

where K: PartialEq,

Count of distinct keys (iter_unique().count()).

Trait Implementations

impl<'a, K: Clone, V: Clone> Clone for MapView<'a, K, V>

fn clone(&self) -> MapView<'a, K, V>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a, K: Debug, V: Debug> Debug for MapView<'a, K, V>

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

Formats the value using the given formatter.

impl<'a, K, V> Default for MapView<'a, K, V>

fn default() -> Self

Returns the “default value” for a type.

impl<'a, K: Eq, V: Eq> Eq for MapView<'a, K, V>

impl<'a, K, V> From<Vec<(K, V)>> for MapView<'a, K, V>

fn from(entries: Vec<(K, V)>) -> Self

Converts to this type from the input type.

impl<'a, K, V> FromIterator<(K, V)> for MapView<'a, K, V>

Duplicate keys are kept and all encoded; see MapView::new.

fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> Self

Creates a value from an iterator.

impl<'b, 'a, K, V> IntoIterator for &'b MapView<'a, K, V>

type Item = &'b (K, V)

The type of the elements being iterated over.

type IntoIter = Iter<'b, (K, V)>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, K, V> IntoIterator for MapView<'a, K, V>

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = IntoIter<(K, V)>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, K: PartialEq, V: PartialEq> PartialEq for MapView<'a, K, V>

fn eq(&self, other: &MapView<'a, K, V>) -> bool

Equality operator ==.

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

Inequality operator !=.

impl<'a, K: PartialEq, V: PartialEq> StructuralPartialEq for MapView<'a, K, V>