From 098704ac22fc571f239667e5504d33640b3a7772 Mon Sep 17 00:00:00 2001
From: p-zach <porterdzach@gmail.com>
Date: Tue, 15 Apr 2025 18:19:25 -0400
Subject: [PATCH] Wrap VariableIndex.at(), .empty()

---
 gtsam/inference/VariableIndex.cpp | 18 ++++++++++++++++++
 gtsam/inference/VariableIndex.h   | 16 ++++------------
 gtsam/inference/inference.i       |  3 +++
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/gtsam/inference/VariableIndex.cpp b/gtsam/inference/VariableIndex.cpp
index 53d400223..3d22501b3 100644
--- a/gtsam/inference/VariableIndex.cpp
+++ b/gtsam/inference/VariableIndex.cpp
@@ -23,6 +23,24 @@ namespace gtsam {
 
 using namespace std;
 
+const FactorIndices& operator[](Key variable) const {
+  KeyMap::const_iterator item = index_.find(variable);
+}
+
+const FactorIndices& at(Key variable) const {
+  KeyMap::const_iterator item = (*this)[variable];
+  if(item == index_.end())
+    throw std::invalid_argument("Requested non-existent variable '" +
+                                DefaultKeyFormatter(variable) +
+                                "' from VariableIndex");
+  else
+    return item->second;
+}
+
+bool empty(Key variable) const {
+  return (*this)[variable].empty();
+}
+
 /* ************************************************************************* */
 bool VariableIndex::equals(const VariableIndex& other, double tol) const {
   return this->nEntries_ == other.nEntries_ && this->nFactors_ == other.nFactors_
diff --git a/gtsam/inference/VariableIndex.h b/gtsam/inference/VariableIndex.h
index 2f872b25d..9885cb1cb 100644
--- a/gtsam/inference/VariableIndex.h
+++ b/gtsam/inference/VariableIndex.h
@@ -84,20 +84,12 @@ class GTSAM_EXPORT VariableIndex {
   size_t nEntries() const { return nEntries_; }
 
   /// Access a list of factors by variable
-  const FactorIndices& operator[](Key variable) const {
-    KeyMap::const_iterator item = index_.find(variable);
-    if(item == index_.end())
-      throw std::invalid_argument("Requested non-existent variable '" +
-                                  DefaultKeyFormatter(variable) +
-                                  "' from VariableIndex");
-    else
-      return item->second;
-  }
+  const FactorIndices& operator[](Key variable) const;
+
+  const FactorIndices& at(Key variable) const;
 
   /// Return true if no factors associated with a variable
-  bool empty(Key variable) const {
-    return (*this)[variable].empty();
-  }
+  bool empty(Key variable) const;
 
   /// @}
   /// @name Testable
diff --git a/gtsam/inference/inference.i b/gtsam/inference/inference.i
index 13c4c9853..084d97a01 100644
--- a/gtsam/inference/inference.i
+++ b/gtsam/inference/inference.i
@@ -199,6 +199,9 @@ class VariableIndex {
   VariableIndex(const T& factorGraph);
   VariableIndex(const gtsam::VariableIndex& other);
 
+  const FactorIndices& at(Key variable) const;
+  bool empty(Key variable) const;
+
   // Testable
   bool equals(const gtsam::VariableIndex& other, double tol) const;
   void print(string s = "VariableIndex: ",