Add documentation for models::append_graph module

src/models/append_graph.rs

@@ -1,13 +1,24 @@
 use crate::maps::{EdgeMap, VertexMap};
 use crate::traits::{GraphTopology, IncidenceCursor};
 
+/// An opaque handle identifying a vertex in an [`AppendGraph`].
+///
+/// Handles are stable for the lifetime of the graph. They can be obtained via graph methods like
+/// [`GraphTopology::add_vertex`] and [`GraphTopology::vertices`].
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct Vertex(usize);
 
+/// An opaque handle identifying an edge in an [`AppendGraph`].
+///
+/// Handles are stable for the lifetime of the graph. They can be obtained via graph methods like
+/// [`GraphTopology::add_edge`] and [`GraphTopology::edges`].
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct Edge(usize);
 
+/// A [`VertexMap`] for [`AppendGraph`] vertices.
 pub type AppendGraphVertexMap<T> = VertexMap<Vertex, T>;
+
+/// An [`EdgeMap`] for [`AppendGraph`] edges.
 pub type AppendGraphEdgeMap<T> = EdgeMap<Edge, T>;
 
 impl Edge {
@@ -16,6 +27,7 @@ impl Edge {
     }
 }
 
+// TODO: Check if VertexIncidenceHeader and IncidenceEntry can be made smaller. Currently they both take 24 bytes (on 64bit), see https://stackoverflow.com/a/79653173
 struct VertexIncidenceHeader {
     incidence_count: usize,
     first_incidence: Option<Edge>,
@@ -27,6 +39,10 @@ struct IncidenceEntry {
     adjacent: Vertex,
 }
 
+/// A resumable cursor over the incidences of a single vertex in an [`AppendGraph`].
+///
+/// Can be obtained via [`GraphTopology::incidence_cursor`]. See [`IncidenceCursor`] on how to use
+/// it.
 #[derive(Copy, Clone)]
 pub struct AppendGraphIncidenceCursor {
     incidence: Option<Edge>,
@@ -38,12 +54,45 @@ impl IncidenceCursor<AppendGraph> for AppendGraphIncidenceCursor {
     }
 }
 
+/// An undirected graph that supports adding vertices and edges, but not deleting them.
+///
+/// `AppendGraph` is optimised for workloads that incrementally build a graph and query it
+/// repeatedly. [`Vertex`]
+/// and [`Edge`] handles are never invalidated. Use [`Graph`] instead if you need to remove vertices
+/// or edges.
+///
+/// Incidences are stored as interlaced adjacency lists in a single flat [`Vec`]. This means that
+/// vertex neighborhood traversals in general result in scattered index jumps.
+///
+/// # Examples
+///
+/// ```
+/// use grapherity::prelude::*;
+/// use grapherity::models::AppendGraph;
+///
+/// let mut graph = AppendGraph::new();
+/// let v1 = graph.add_vertex();
+/// let v2 = graph.add_vertex();
+/// let e = graph.add_edge(v1, v2);
+/// assert!(graph.are_adjacent(v1, v2));
+/// ```
+///
+///  # Time and space complexity
+///
+/// Both [`add_vertex`] and [`add_edge`] run in amortised *O(1)* time. [`degree`] runs in *O(1)*
+/// time since vertex degrees are stored. Space complexity is *O(|V| + |E|)*.
+///
+/// [`add_vertex`]: Self::add_vertex
+/// [`add_edge`]: Self::add_edge
+/// [`degree`]: Self::degree
+/// [`Graph`]: crate::models::Graph
 pub struct AppendGraph {
     vertices: Vec<VertexIncidenceHeader>,
     incidences: Vec<IncidenceEntry>,
 }
 
 impl AppendGraph {
+    /// Creates an empty graph instance with no vertices or edges.
     pub fn new() -> Self {
         Self {
             vertices: vec![],
@@ -51,8 +100,8 @@ impl AppendGraph {
         }
     }
 
-    // Adds a single incidence of an edge, which is composed by two such incidences, to the
+    /// Adds a single incidence of an edge, which is composed by two such incidences, to the
-    // incidences vector.
+    /// incidences vector.
     fn add_incidence(&mut self, v1: Vertex, v2: Vertex) {
         self.incidences.push(IncidenceEntry {
             next: self.vertices[v1.0].first_incidence.take(),