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Refactor ElementMap, removing its copy-on-write feature

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warrence
2026-10-11 22:24:00 +02:00
parent 4e20c49486
commit 3d7dda6f7b
9 changed files with 281 additions and 113 deletions
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README.md
+3 -3
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@@ -7,7 +7,7 @@ This crate provides data structures to model graphs and to perform algorithms on
Currently supported are:
* Undirected graph types `Graph`, `AppendGraph`, and `FrozenGraph`, built on a flat, index-based adjacency list,
* Maps to freely associate custom data with vertices and edges,
* `ElementMap` to freely associate custom data with vertices and edges,
* Connectivity and pathing algorithms: Dijkstra's algorithm, DFS, and BFS in different variants,
* Exposed traits to implement custom graph data structures or algorithms.
@@ -22,14 +22,14 @@ use grapherity::models::Graph;
use grapherity::algorithms;
let mut graph = Graph::new();
// Creates a map for edge weights with a default weight.
let mut weights = graph.edge_map(1);
// Adds three vertices and two edges.
let v1 = graph.add_vertex();
let v2 = graph.add_vertex();
let v3 = graph.add_vertex();
graph.add_edge(v1, v2);
let e = graph.add_edge(v2, v3);
// Creates a map for edge weights with a default weight, after creating the edge.
let mut weights = graph.edge_map(1);
// Sets a non-default weight for the second edge.
weights[e] = 5;
src/lib.rs
+4 -3
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@@ -23,14 +23,14 @@
//! use grapherity::algorithms;
//!
//! let mut graph = Graph::new();
//! // Creates a map for edge weights with a default weight.
//! let mut weights = graph.edge_map(1);
//! // Adds three vertices and two edges.
//! let v1 = graph.add_vertex();
//! let v2 = graph.add_vertex();
//! let v3 = graph.add_vertex();
//! graph.add_edge(v1, v2);
//! let e = graph.add_edge(v2, v3);
//! // Creates a map for edge weights with a default weight, after creating the edges.
//! let mut weights = graph.edge_map(1);
//! // Sets a non-default weight for the second edge.
//! weights[e] = 5;
//!
@@ -97,7 +97,8 @@
//! graph.degree(v);
//! ```
//!
//! [`ElementMap`] is not required to panic if provided with an invalid vertex or edge.
//! [`ElementMap`] does not check validity of vertices or edges and might or might not panic in case
//! an invalid handle is provided.
//!
//! Vertices and edges are provided by the graph and not intended to be generated by users.
//!
src/maps.rs
+113 -76
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@@ -1,7 +1,7 @@
//! Provides maps to associate custom data to graph vertices and edges.
//!
//! [`ElementMap`] provides a copy-on-write, [`Vec`]-backed map to associate data to either all
//! vertices or all edges in a graph.
//! [`ElementMap`] is a dense, [`Vec`]-backed map to associate data to either all vertices or all
//! edges in a graph.
use std::ops::{Index, IndexMut};
@@ -12,15 +12,19 @@ use std::ops::{Index, IndexMut};
/// which means that the provided index conversion function should map elements to contiguous
/// indices, or indices with relatively few gaps.
///
/// Data allocation happens as copy-on-write, i.e. the backing [`Vec`] is only resized if a value is
/// written beyond current capacity, but the `default` value can transparently be read. No bound or
/// validity checks are performed by the map on the provided element handles.
///
/// Use [`GraphTopology::vertex_map`] or [`GraphTopology::edge_map`] to obtain an `ElementMap` for
/// vertices or edges, respectively.
///
/// The map does not grow on its own when the associated graph grows. Use the graph's
/// [`GraphTopologyAddition::sync_vertex_map`] or [`GraphTopologyAddition::sync_edge_map`] to extend
/// the map explicitly after adding vertices or edges to it.
///
/// No bound or validity checks are performed by the map on the provided element handles.
///
/// [`GraphTopology::edge_map`]: crate::traits::GraphTopology::edge_map
/// [`GraphTopology::vertex_map`]: crate::traits::GraphTopology::vertex_map
/// [`GraphTopologyAddition::sync_vertex_map`]: crate::traits::GraphTopologyAddition::sync_vertex_map
/// [`GraphTopologyAddition::sync_edge_map`]: crate::traits::GraphTopologyAddition::sync_edge_map
pub struct ElementMap<E: Copy, T: Clone> {
data: Vec<T>,
default: T,
@@ -29,47 +33,59 @@ pub struct ElementMap<E: Copy, T: Clone> {
impl<E: Copy, T: Clone> ElementMap<E, T> {
/// Creates a new map with the given `default` value, an index conversion function `to_index`,
/// and an initial `capacity`.
pub fn new(default: T, to_index: fn(E) -> usize, capacity: usize) -> Self {
/// and an initial `len`, i.e. the number of slots that can be read from and written to.
///
/// Since `to_index` is usually an implementation detail of the graph model, this is not meant
/// to be called directly. Use [`GraphTopology::vertex_map`] or [`GraphTopology::edge_map`]
/// instead.
///
/// [`GraphTopology::edge_map`]: crate::traits::GraphTopology::edge_map
/// [`GraphTopology::vertex_map`]: crate::traits::GraphTopology::vertex_map
pub fn new(default: T, to_index: fn(E) -> usize, len: usize) -> Self {
Self {
data: vec![default.clone(); capacity],
data: vec![default.clone(); len],
default,
to_index,
}
}
/// Returns the total number of data entries the map can write without reallocating. Reads
/// beyond `capacity` are valid and return the default value.
pub fn capacity(&self) -> usize {
self.data.capacity()
}
/// Reserves capacity for at least `additional` more data entries. Does nothing if capacity is
/// already sufficient.
/// Grows the map so that it contains at least `new_len` slots for elements, initialising any
/// newly added slots to the `default` value provided to [`new`], without modifying existing
/// data. Does nothing if the map already has at least `new_len` slots.
///
/// Use this before writing data for new graph elements to avoid incremental growth on the first
/// write to each new element.
pub fn reserve(&mut self, additional: usize) {
self.data.reserve(additional);
/// Since the number of elements the map can actually store depend on the index conversion
/// function, which is usually an implementation detail of the graph model, this is not meant to
/// be called directly. Use [`GraphTopologyAddition::sync_vertex_map`] or
/// [`GraphTopologyAddition::sync_edge_map`] instead.
///
/// [`new`]: ElementMap::new
/// [`GraphTopologyAddition::sync_vertex_map`]: crate::traits::GraphTopologyAddition::sync_vertex_map
/// [`GraphTopologyAddition::sync_edge_map`]: crate::traits::GraphTopologyAddition::sync_edge_map
pub fn grow(&mut self, new_len: usize) {
if new_len > self.data.len() {
self.data.resize(new_len, self.default.clone());
}
}
/// Returns a new map over the same elements with values transformed by `f`.
///
/// The default value of the new map is `f` applied to the original default, so reads beyond the
/// current capacity of the new map behave consistently with the transformation.
/// The default value of the new map is `f` applied to the original default, so slots later added
/// to the new map by [`GraphTopologyAddition::sync_vertex_map`] or
/// [`GraphTopologyAddition::sync_edge_map`] are filled consistently with the transformation.
///
/// [`GraphTopologyAddition::sync_vertex_map`]: crate::traits::GraphTopologyAddition::sync_vertex_map
/// [`GraphTopologyAddition::sync_edge_map`]: crate::traits::GraphTopologyAddition::sync_edge_map
///
/// # Examples
///
/// ```
/// # use grapherity::maps::ElementMap;
/// let mut map: ElementMap<usize, Option<i32>> = ElementMap::new(None, |e| e, 0);
/// let mut map: ElementMap<usize, Option<i32>> = ElementMap::new(None, |e| e, 2);
/// map[1] = Some(42);
///
/// let bools = map.map(|v| v.is_some());
/// assert_eq!(bools[0], false);
/// assert_eq!(bools[1], true);
/// // Returns mapped default for reads beyond capacity.
/// assert_eq!(bools[9], false);
/// ```
pub fn map<U: Clone>(&self, f: impl Fn(&T) -> U) -> ElementMap<E, U> {
ElementMap {
@@ -84,22 +100,13 @@ impl<E: Copy, T: Clone> Index<E> for ElementMap<E, T> {
type Output = T;
fn index(&self, e: E) -> &T {
let i = (self.to_index)(e);
if i < self.data.len() {
&self.data[i]
} else {
&self.default
}
&self.data[(self.to_index)(e)]
}
}
impl<E: Copy, T: Clone> IndexMut<E> for ElementMap<E, T> {
fn index_mut(&mut self, e: E) -> &mut T {
let i = (self.to_index)(e);
if i >= self.data.len() {
self.data.resize(i + 1, self.default.clone());
}
&mut self.data[i]
&mut self.data[(self.to_index)(e)]
}
}
@@ -109,67 +116,97 @@ mod tests {
#[test]
fn initial_values_are_default() {
let map = ElementMap::new(42, |e| e, 0);
let map = ElementMap::new(42, |e| e, 6);
assert_eq!(map[0], 42, "initial read at 0 should be default");
assert_eq!(map[5], 42, "initial read at 5 should be default");
}
#[test]
fn reserve_increases_capacity_without_initializing() {
let mut map = ElementMap::new(0, |e| e, 0);
let capacity_before = map.capacity();
map.reserve(capacity_before + 10);
assert!(
map.capacity() > capacity_before,
"expected sufficient capacity increase after reserve"
);
assert_eq!(map[5], 0, "expected read beyond length to return default");
#[should_panic]
fn read_out_of_bounds() {
let map = ElementMap::new(42, |e| e, 3);
let _ = map[3];
}
#[test]
fn reserve_prevents_reallocation_on_write() {
let mut map = ElementMap::new(0, |e| e, 0);
map.reserve(10);
let capacity_before = map.capacity();
for i in 0..10 {
map[i] = i as i32;
}
assert_eq!(
map.capacity(),
capacity_before,
"writes within reserved capacity should not reallocate"
);
}
#[test]
fn reserve_does_not_overwrite_existing_values() {
let mut map = ElementMap::new(0, |e| e, 0);
map[0] = 5;
let capacity_before = map.capacity();
map.reserve(capacity_before + 10);
assert_eq!(map[0], 5, "reserve should not change existing data");
#[should_panic]
fn write_out_of_bounds() {
let mut map = ElementMap::new(0, |e| e, 3);
map[3] = 1;
}
#[test]
fn write_and_read() {
let mut map = ElementMap::new(0, |e| e, 0);
let mut map = ElementMap::new(0, |e| e, 2);
map[1] = 7;
assert_eq!(map[1], 7, "unexpected read value after write");
assert_eq!(map[0], 0, "initial read should be default");
}
#[test]
fn grow() {
let mut map = ElementMap::new(0, |e| e, 2);
assert_eq!(
map.data.len(),
2,
"precondition: unexpected data length before grow"
);
map.grow(10);
assert_eq!(map.data.len(), 10, "unexpected data length after grow");
}
#[test]
fn grow_extends_with_default() {
let mut map = ElementMap::new(17, |e| e, 3);
map.grow(6);
assert_eq!(map[5], 17, "read of newly grown slot should be default");
map[5] = 9;
assert_eq!(
map[5], 9,
"unexpected value after write in newly grown slot"
);
}
#[test]
fn grow_preserves_existing_values() {
let mut map = ElementMap::new(22, |e| e, 3);
map[0] = 5;
map.grow(10);
assert_eq!(map[0], 5, "unexpected data after grow");
}
#[test]
fn grow_to_smaller_len() {
let mut map = ElementMap::new(23, |e| e, 6);
map[5] = 9;
map.grow(3);
assert_eq!(
map[5], 9,
"grow to a smaller length should not discard data"
);
assert_eq!(map.data.len(), 6, "unexpected data length");
}
#[test]
fn map() {
let mut source: ElementMap<usize, Option<i32>> = ElementMap::new(None, |e| e, 0);
let mut source: ElementMap<usize, Option<i32>> = ElementMap::new(None, |e| e, 3);
source[1] = Some(42);
source[2] = None;
let mapped = source.map(|v| v.is_some());
assert_eq!(mapped[0], false, "unset entry should map to false");
assert_eq!(mapped[1], true, "Some entry should map to true");
assert_eq!(mapped[2], false, "explicit None entry should map to false");
assert_eq!(
mapped[9], false,
"read beyond capacity should return mapped default"
assert!(!mapped[0], "unset entry should map to false");
assert!(mapped[1], "Some entry should map to true");
assert!(!mapped[2], "explicit None entry should map to false");
}
#[test]
fn map_grow() {
let mut source: ElementMap<usize, Option<i32>> = ElementMap::new(None, |e| e, 2);
source[1] = Some(42);
let mut mapped = source.map(|v| v.is_some());
mapped.grow(4);
assert!(
!mapped[3],
"slot added by grow should hold the mapped default"
);
}
}
src/models/append_graph.rs
-2
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@@ -170,7 +170,6 @@ impl GraphTopology for AppendGraph {
self.vertices.len()
}
// TODO: Create with capacity 0, maybe offer pre-allocated alternative?
fn vertex_map<T: Clone>(&self, default: T) -> ElementMap<Self::Vertex, T> {
ElementMap::new(default, |v| v.0, self.vertex_capacity())
}
@@ -179,7 +178,6 @@ impl GraphTopology for AppendGraph {
self.incidences.len() / 2
}
// TODO: Create with capacity 0, maybe offer pre-allocated alternative?
fn edge_map<T: Clone>(&self, default: T) -> ElementMap<Self::Edge, T> {
ElementMap::new(default, |e| e.index() / 2, self.edge_capacity())
}
src/models/frozen_graph.rs
+2 -1
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@@ -144,7 +144,8 @@ impl GraphTopology for FrozenGraph {
// TODO: Find a way to reduce the needed capacity for the edge ElementMap. This could be improved by finding a small vertex cover and store those vertices first. See https://en.wikipedia.org/wiki/Vertex_cover#Approximate_evaluation
fn edge_map<T: Clone>(&self, default: T) -> ElementMap<Self::Edge, T> {
ElementMap::new(default, |e| e.0, self.incidences.len() - 1)
// "incidences.len() - 1" would underflow for an edge-free graph.
ElementMap::new(default, |e| e.0, self.incidences.len().saturating_sub(1))
}
fn degree(&self, v: Self::Vertex) -> usize {
src/models/graph.rs
-2
View File
@@ -262,7 +262,6 @@ impl GraphTopology for Graph {
self.vertices.len()
}
// TODO: Create with capacity 0, maybe offer pre-allocated alternative?
fn vertex_map<T: Clone>(&self, default: T) -> ElementMap<Self::Vertex, T> {
ElementMap::new(default, |v| v.arr_idx(), self.vertex_capacity())
}
@@ -271,7 +270,6 @@ impl GraphTopology for Graph {
self.incidences.len() / 2
}
// TODO: Create with capacity 0, maybe offer pre-allocated alternative?
fn edge_map<T: Clone>(&self, default: T) -> ElementMap<Self::Edge, T> {
ElementMap::new(default, |e| e.arr_idx() / 2, self.edge_capacity())
}
src/testing/graph_topology_addition_testing.rs
+47 -8
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@@ -15,8 +15,10 @@ macro_rules! graph_topology_addition_tests {
reserve_edges_does_not_affect_vertex_capacity,
add_vertex,
add_edge,
vertex_map_new_vertex,
edge_map_new_edge,
sync_vertex_map_after_add,
sync_edge_map_after_add,
sync_vertex_map_preserves_values,
sync_edge_map_preserves_values,
);
};
@@ -122,31 +124,68 @@ where
assert_ne!(graph.add_edge(u, v), e, "unexpected duplicate edge");
}
pub fn vertex_map_new_vertex<G: GraphTopologyAddition>() {
pub fn sync_vertex_map_after_add<G: GraphTopologyAddition>() {
let mut graph = G::default();
let mut map = graph.vertex_map(27);
let u = graph.add_vertex();
let v = graph.add_vertex();
graph.sync_vertex_map(&mut map);
assert_eq!(
map[v], 27,
map[u], 27,
"unexpected value from default map read for new vertex"
);
map[v] = 9;
map[u] = 9;
assert_eq!(
map[v], 9,
map[u], 9,
"unexpected value from map read after write for new vertex"
);
assert_eq!(
map[v], 27,
"unexpected value from default map read for second new vertex"
);
}
pub fn edge_map_new_edge<G: GraphTopologyAddition>() {
pub fn sync_edge_map_after_add<G: GraphTopologyAddition>() {
let mut graph = G::default();
let u = graph.add_vertex();
let v = graph.add_vertex();
let mut map = graph.edge_map(28);
let e = graph.add_edge(u, v);
assert_eq!(map[e], 28);
let f = graph.add_edge(u, v);
graph.sync_edge_map(&mut map);
assert_eq!(
map[e], 28,
"unexpected value from default map read for new edge"
);
map[e] = 8;
assert_eq!(
map[e], 8,
"unexpected value from map read after write for new edge"
);
assert_eq!(
map[f], 28,
"unexpected value from default map read for second new edge"
);
}
pub fn sync_vertex_map_preserves_values<G: GraphTopologyAddition>() {
let mut graph = G::default();
let v = graph.add_vertex();
let mut map = graph.vertex_map(0);
map[v] = 5;
graph.reserve_vertices(20);
graph.sync_vertex_map(&mut map);
assert_eq!(map[v], 5, "sync should not change existing map values");
}
pub fn sync_edge_map_preserves_values<G: GraphTopologyAddition>() {
let mut graph = G::default();
let u = graph.add_vertex();
let v = graph.add_vertex();
let e = graph.add_edge(u, v);
let mut map = graph.edge_map(0);
map[e] = 6;
graph.reserve_edges(20);
graph.sync_edge_map(&mut map);
assert_eq!(map[e], 6, "sync should not change existing map values");
}
src/testing/graph_topology_testing.rs
+32 -12
View File
@@ -72,12 +72,22 @@ pub fn vertex_count<G: MakeTestGraph>() {
assert_eq!(graph.vertex_count(), 10, "unexpected vertex count");
}
pub fn vertex_map<G: MakeTestGraph>() {
let (graph, v) = G::single_vertex();
let mut map = graph.vertex_map(27);
assert_eq!(map[v], 27, "unexpected value from default map read");
map[v] = 9;
assert_eq!(map[v], 9, "unexpected value from map after write");
pub fn vertex_map<G: MakeTestGraph>()
where
G::Vertex: Debug,
{
let (graph, vertices, _, _) = G::standard();
let mut map = graph.vertex_map(88);
for (i, &v) in vertices.iter().enumerate() {
assert_eq!(
map[v], 88,
"unexpected value from default map read for vertex {v:?}"
);
map[v] = i;
}
for (i, &v) in vertices.iter().enumerate() {
assert_eq!(map[v], i, "unexpected value after write for vertex {v:?}");
}
}
pub fn edge_count_empty<G: MakeTestGraph>() {
@@ -90,12 +100,22 @@ pub fn edge_count<G: MakeTestGraph>() {
assert_eq!(graph.edge_count(), 18, "unexpected edge count");
}
pub fn edge_map<G: MakeTestGraph>() {
let (graph, _, e) = G::single_edge();
let mut map = graph.edge_map(28);
assert_eq!(map[e], 28, "unexpected value from default map read");
map[e] = 8;
assert_eq!(map[e], 8, "unexpected value from map after write");
pub fn edge_map<G: MakeTestGraph>()
where
G::Edge: Debug,
{
let (graph, _, edges, _) = G::standard();
let mut map = graph.edge_map(99);
for (i, &(e, _, _)) in edges.iter().enumerate() {
assert_eq!(
map[e], 99,
"unexpected value from default map read for edge {e:?}"
);
map[e] = i;
}
for (i, &(e, _, _)) in edges.iter().enumerate() {
assert_eq!(map[e], i, "unexpected value after write for edge {e:?}");
}
}
pub fn degree_zero<G: MakeTestGraph>() {
src/traits.rs
+80 -6
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@@ -47,6 +47,10 @@ pub trait GraphTopology {
/// Creates and returns an [`ElementMap`] for the vertices with every slot initialised to
/// `default`.
///
/// The returned map only covers the vertices that exist in the graph at the time of the call.
/// Use [`GraphTopologyAddition::sync_vertex_map`] to extend the map before accessing new
/// vertices.
///
/// # Examples
///
/// ```
@@ -54,13 +58,11 @@ pub trait GraphTopology {
/// # use grapherity::models::Graph;
/// let mut graph = Graph::new();
/// let v1 = graph.add_vertex();
/// let v2 = graph.add_vertex();
/// let mut labels = graph.vertex_map("z");
/// assert_eq!(labels[v1], "z");
/// labels[v1] = "a";
/// assert_eq!(labels[v1], "a");
///
/// // A new vertex is immediately available for read and write.
/// let v2 = graph.add_vertex();
/// assert_eq!(labels[v2], "z");
/// labels[v2] = "b";
/// assert_eq!(labels[v2], "b");
@@ -72,6 +74,9 @@ pub trait GraphTopology {
/// Creates and returns an [`ElementMap`] for the edges with every slot initialised to `default`.
///
/// The returned map only covers the edges that exist in the graph at the time of the call. Use
/// [`GraphTopologyAddition::sync_edge_map`] to extend the map before accessing new edges.
///
/// # Examples
///
/// ```
@@ -81,13 +86,11 @@ pub trait GraphTopology {
/// let v1 = graph.add_vertex();
/// let v2 = graph.add_vertex();
/// let e1 = graph.add_edge(v1, v2);
/// let e2 = graph.add_edge(v1, v2);
/// let mut weights = graph.edge_map(5);
/// assert_eq!(weights[e1], 5);
/// weights[e1] = 1;
/// assert_eq!(weights[e1], 1);
///
/// // A new edge is immediately available for read and write.
/// let e2 = graph.add_edge(v1, v2);
/// assert_eq!(weights[e2], 5);
/// weights[e2] = 2;
/// assert_eq!(weights[e2], 2);
@@ -180,9 +183,21 @@ pub trait GraphTopology {
/// undirected graph.
pub trait GraphTopologyAddition: GraphTopology + Default {
/// Returns the total number of vertices the graph can hold without reallocating.
///
/// For every valid [`Vertex`] handle, the index produced by the conversion function used in
/// [`GraphTopology::vertex_map`] must be strictly less than this capacity. Implementors of
/// [`GraphTopology::vertex_map`] must size the returned vertex [`ElementMap`] to this capacity.
///
/// [`Vertex`]: GraphTopology::Vertex
fn vertex_capacity(&self) -> usize;
/// Returns the total number of edges the graph can hold without reallocating.
///
/// For every valid [`Edge`] handle, the index produced by the conversion function used in
/// [`GraphTopology::edge_map`] must be strictly less than this capacity. Implementors of
/// [`GraphTopology::edge_map`] must size the returned edge [`ElementMap`] to this capacity.
///
/// [`Edge`]: GraphTopology::Edge
fn edge_capacity(&self) -> usize;
/// Reserves capacity for at least `additional` more vertices. Does nothing if capacity is
@@ -212,6 +227,65 @@ pub trait GraphTopologyAddition: GraphTopology + Default {
///
/// Panics if `u` or `v` is not a valid vertex of this graph.
fn add_edge(&mut self, u: Self::Vertex, v: Self::Vertex) -> Self::Edge;
/// Grows `map` so that it covers a number of vertices up to at least [`vertex_capacity`].
///
/// The data for any newly covered vertices is initialised to the map's original default value.
/// Does nothing if `map` already covers enough vertices.
///
/// An [`ElementMap`] does not grow on its own, so call this after [`reserve_vertices`] (or
/// after vertices have already been added) and before accessing `map` for any newly added
/// vertices.
///
/// # Examples
///
/// ```
/// # use grapherity::prelude::*;
/// # use grapherity::models::Graph;
/// let mut graph = Graph::new();
/// let mut labels = graph.vertex_map("z");
/// graph.reserve_vertices(1);
/// graph.sync_vertex_map(&mut labels);
/// let v = graph.add_vertex();
/// labels[v] = "a";
/// assert_eq!(labels[v], "a");
/// ```
///
/// [`reserve_vertices`]: Self::reserve_vertices
/// [`vertex_capacity`]: Self::vertex_capacity
fn sync_vertex_map<T: Clone>(&self, map: &mut ElementMap<Self::Vertex, T>) {
map.grow(self.vertex_capacity());
}
/// Grows `map` so that it covers a number of edges up to at least [`edge_capacity`].
///
/// The data for any newly covered edges is initialised to the map's original default value.
/// Does nothing if `map` already covers enough edges.
///
/// An [`ElementMap`] does not grow on its own, so call this after [`reserve_edges`] (or after
/// edges have already been added) and before accessing `map` for any newly added edges.
///
/// # Examples
///
/// ```
/// # use grapherity::prelude::*;
/// # use grapherity::models::Graph;
/// let mut graph = Graph::new();
/// let mut weights = graph.edge_map(1);
/// let v1 = graph.add_vertex();
/// let v2 = graph.add_vertex();
/// graph.reserve_edges(1);
/// graph.sync_edge_map(&mut weights);
/// let e = graph.add_edge(v1, v2);
/// weights[e] = 5;
/// assert_eq!(weights[e], 5);
/// ```
///
/// [`reserve_edges`]: Self::reserve_edges
/// [`edge_capacity`]: Self::edge_capacity
fn sync_edge_map<T: Clone>(&self, map: &mut ElementMap<Self::Edge, T>) {
map.grow(self.edge_capacity());
}
}
/// A trait that adds deletion operations to an undirected graph topology.