Add ErrVertexNotFound error (#60)

CHANGELOG.md

@@ -7,9 +7,13 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [0.14.0] - 2022-11-01
 
+### Added
+* Added the `ErrVertexNotFound` error instance.
+
 ### Changed
 * Changed `TopologicalSort` to fail at runtime when a cycle is detected.
 * Changed `TransitiveReduction` to return the transitive reduction as a new graph and fail at runtime when a cycle is detected.
+* Changed `Vertex` to return `ErrVertexNotFound` if the desired vertex couldn't be found.
 
 ## [0.13.0] - 2022-10-15
 

directed.go

@@ -49,7 +49,7 @@ func (d *directed[K, T]) AddVertex(value T, options ...func(*VertexProperties))
 func (d *directed[K, T]) Vertex(hash K) (T, error) {
 	vertex, ok := d.vertices[hash]
 	if !ok {
-		return vertex, fmt.Errorf("vertex with hash %v doesn't exist", hash)
+		return vertex, ErrVertexNotFound
 	}
 
 	return vertex, nil

graph.go

@@ -4,8 +4,12 @@ package graph
 
 import "errors"
 
-// ErrEdgeNotFound will be returned when a desired edge cannot be found.
-var ErrEdgeNotFound = errors.New("edge not found")
+var (
+	// ErrVertexNotFound will be returned when a desired vertex cannot be found.
+	ErrVertexNotFound = errors.New("vertex not found")
+	// ErrEdgeNotFound will be returned when a desired edge cannot be found.
+	ErrEdgeNotFound = errors.New("edge not found")
+)
 
 // Graph represents a generic graph data structure consisting of vertices and edges. Its vertices
 // are of type T, and each vertex is identified by a hash of type K.
@@ -26,7 +30,7 @@ type Graph[K comparable, T any] interface {
 	//
 	AddVertex(value T, options ...func(*VertexProperties)) error
 
-	// Vertex returns the vertex with the given hash or an error if the vertex doesn't exist.
+	// Vertex returns the vertex with the given hash or ErrVertexNotFound if it doesn't exist.
 	Vertex(hash K) (T, error)
 
 	// VertexWithProperties returns the vertex with the given hash along with its properties, or an

undirected.go

@@ -47,7 +47,7 @@ func (u *undirected[K, T]) AddVertex(value T, options ...func(*VertexProperties)
 func (u *undirected[K, T]) Vertex(hash K) (T, error) {
 	vertex, ok := u.vertices[hash]
 	if !ok {
-		return vertex, fmt.Errorf("vertex with hash %v doesn't exist", hash)
+		return vertex, ErrVertexNotFound
 	}
 
 	return vertex, nil