From de5262fcc97ddceedee98685f23fdec88ec5f754 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 28 Sep 2023 10:50:05 +0200
Subject: [PATCH 1/4] Add assertion

---
 crates/fj-core/src/objects/handles.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crates/fj-core/src/objects/handles.rs b/crates/fj-core/src/objects/handles.rs
index d9ee8b6a5..fa6af5085 100644
--- a/crates/fj-core/src/objects/handles.rs
+++ b/crates/fj-core/src/objects/handles.rs
@@ -71,6 +71,8 @@ impl<T> Handles<T> {
     /// If the length of `Handles` is `i`, then retrieving the i-th edge using
     /// this method, is the same as retrieving the 0-th one.
     pub fn nth_circular(&self, index: usize) -> &Handle<T> {
+        assert!(!self.is_empty(), "`Handles` must not be empty");
+
         let index = index % self.len();
         self.nth(index)
             .expect("Index must be valid, due to modulo above")

From d114e4375f06f6261a607d60a8778839ff7c5bb3 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 28 Sep 2023 10:50:56 +0200
Subject: [PATCH 2/4] Update doc comment

---
 crates/fj-core/src/objects/handles.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/crates/fj-core/src/objects/handles.rs b/crates/fj-core/src/objects/handles.rs
index fa6af5085..a17ba356a 100644
--- a/crates/fj-core/src/objects/handles.rs
+++ b/crates/fj-core/src/objects/handles.rs
@@ -70,6 +70,10 @@ impl<T> Handles<T> {
     ///
     /// If the length of `Handles` is `i`, then retrieving the i-th edge using
     /// this method, is the same as retrieving the 0-th one.
+    ///
+    /// # Panics
+    ///
+    /// Panics, if `Handles` is empty.
     pub fn nth_circular(&self, index: usize) -> &Handle<T> {
         assert!(!self.is_empty(), "`Handles` must not be empty");
 

From 8f40971d94536499923661564c3809c3b09cf379 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Wed, 27 Sep 2023 10:38:10 +0200
Subject: [PATCH 3/4] Add `Handles::only`

---
 crates/fj-core/src/objects/handles.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/crates/fj-core/src/objects/handles.rs b/crates/fj-core/src/objects/handles.rs
index a17ba356a..eb4085ebc 100644
--- a/crates/fj-core/src/objects/handles.rs
+++ b/crates/fj-core/src/objects/handles.rs
@@ -61,6 +61,25 @@ impl<T> Handles<T> {
         self.inner.is_empty()
     }
 
+    /// Return the only item
+    ///
+    /// # Panics
+    ///
+    /// Panics, if there is more than one item.
+    pub fn only(&self) -> &Handle<T> {
+        let mut iter = self.inner.iter();
+        let item = iter
+            .next()
+            .expect("Requested only item, but no items available");
+
+        assert!(
+            iter.next().is_none(),
+            "Requested only item, but more than one available"
+        );
+
+        item
+    }
+
     /// Return the n-th item
     pub fn nth(&self, index: usize) -> Option<&Handle<T>> {
         self.inner.get(index)

From 1f776e7ff9df1dd2fa34c370f9a84bd8f9ba5173 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Wed, 27 Sep 2023 10:47:32 +0200
Subject: [PATCH 4/4] Add `Handles::first`

---
 crates/fj-core/src/objects/handles.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/crates/fj-core/src/objects/handles.rs b/crates/fj-core/src/objects/handles.rs
index eb4085ebc..4db5a5cd0 100644
--- a/crates/fj-core/src/objects/handles.rs
+++ b/crates/fj-core/src/objects/handles.rs
@@ -80,6 +80,17 @@ impl<T> Handles<T> {
         item
     }
 
+    /// Return the first item
+    ///
+    /// # Panics
+    ///
+    /// Panics, if there are no items.
+    pub fn first(&self) -> &Handle<T> {
+        self.inner
+            .first()
+            .expect("Requested first item, but no items available")
+    }
+
     /// Return the n-th item
     pub fn nth(&self, index: usize) -> Option<&Handle<T>> {
         self.inner.get(index)