1 files changed, 37 insertions, 0 deletions
diff --git a/graph/src/builder.rs b/graph/src/builder.rs
index 9ab5895..4a480a5 100644
--- a/graph/src/builder.rs
+++ b/graph/src/builder.rs
@@ -54,3 +54,40 @@ pub trait Builder: Default {
     /// still be used later on.
     fn build_ref(&self) -> Self::Result;
 }
+
+/// The type of builders that actually reference the underlying graph
+/// instead of owe it.
+///
+/// To finish the task of the builder, just do not use it anymore.
+/// The building happens right when the building methods are called.
+pub trait BuilderMut {
+    /// Some graphs are labelled.  This type should be the type of the
+    /// labels.
+    type Label;
+
+    /// The type of the underlying graph.
+    type Graph: Graph;
+
+    /// The type of the builder from a borrow.
+    type ResultBuilder<'a>: BuilderMut
+    where
+        Self::Label: 'a;
+
+    /// Borrow a graph to create a builder without copying.
+    fn from_graph_mut(graph: &mut Self::Graph) -> Self::ResultBuilder<'_>;
+
+    /// Add a new vertex.
+    fn add_vertex(&mut self, label: Self::Label) -> Result<usize, Error>;
+
+    /// Add an edge from the source to the target.
+    fn add_edge(&mut self, source: usize, target: usize, label: Self::Label) -> Result<(), Error>;
+
+    /// Remove an edge from the source to the target.
+    ///
+    /// Since some graphs are labelled, the users are allowed to pass
+    /// a predicate to determine if an edge from the source to the
+    /// target should be removed.
+    fn remove_edge<F>(&mut self, source: usize, target: usize, predicate: F) -> Result<(), Error>
+    where
+        F: Fn(Self::Label) -> bool;
+}