From 72734d184b28953a14bf150ea13450fad5bba218 Mon Sep 17 00:00:00 2001
From: Varun Agrawal <varagrawal@gmail.com>
Date: Thu, 29 Jun 2023 12:12:48 -0400
Subject: [PATCH] overload += operator in Ordering

---
 gtsam/inference/Ordering.cpp           | 12 ++++++++++++
 gtsam/inference/Ordering.h             | 20 +++++++-------------
 gtsam/inference/tests/testOrdering.cpp | 14 ++++++++++++++
 3 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/gtsam/inference/Ordering.cpp b/gtsam/inference/Ordering.cpp
index 2956c7575..cb2ca752d 100644
--- a/gtsam/inference/Ordering.cpp
+++ b/gtsam/inference/Ordering.cpp
@@ -281,6 +281,18 @@ void Ordering::print(const std::string& str,
   cout.flush();
 }
 
+/* ************************************************************************* */
+Ordering::This& Ordering::operator+=(Key key) {
+  this->push_back(key);
+  return *this;
+}
+
+/* ************************************************************************* */
+Ordering::This& Ordering::operator,(Key key) {
+  this->push_back(key);
+  return *this;
+}
+
 /* ************************************************************************* */
 Ordering::This& Ordering::operator+=(KeyVector& keys) {
   this->insert(this->end(), keys.begin(), keys.end());
diff --git a/gtsam/inference/Ordering.h b/gtsam/inference/Ordering.h
index 884a93f0d..86d44e072 100644
--- a/gtsam/inference/Ordering.h
+++ b/gtsam/inference/Ordering.h
@@ -25,10 +25,6 @@
 #include <gtsam/inference/MetisIndex.h>
 #include <gtsam/base/FastSet.h>
 
-#ifdef GTSAM_USE_BOOST_FEATURES
-#include <boost/assign/list_inserter.hpp>
-#endif
-
 #include <algorithm>
 #include <vector>
 
@@ -61,15 +57,13 @@ public:
       Base(keys.begin(), keys.end()) {
   }
 
-#ifdef GTSAM_USE_BOOST_FEATURES
-  /// Add new variables to the ordering as ordering += key1, key2, ...  Equivalent to calling
-  /// push_back.
-  boost::assign::list_inserter<boost::assign_detail::call_push_back<This> > operator+=(
-      Key key) {
-    return boost::assign::make_list_inserter(
-        boost::assign_detail::call_push_back<This>(*this))(key);
-  }
-#endif
+  /// Add new variables to the ordering as
+  /// `ordering += key1, key2, ...`.
+  This& operator+=(Key key);
+
+  /// Overloading the comma operator allows for chaining appends
+  // e.g. keys += key1, key2
+  This& operator,(Key key);
 
   /**
    * @brief Append new keys to the ordering as `ordering += keys`.
diff --git a/gtsam/inference/tests/testOrdering.cpp b/gtsam/inference/tests/testOrdering.cpp
index 761c330b4..328d383d8 100644
--- a/gtsam/inference/tests/testOrdering.cpp
+++ b/gtsam/inference/tests/testOrdering.cpp
@@ -196,6 +196,20 @@ TEST(Ordering, csr_format_3) {
   EXPECT(adjExpected == adjAcutal);
 }
 
+/* ************************************************************************* */
+TEST(Ordering, AppendKey) {
+  using symbol_shorthand::X;
+  Ordering actual;
+  actual += X(0);
+
+  Ordering expected1{X(0)};
+  EXPECT(assert_equal(expected1, actual));
+
+  actual += X(1), X(2), X(3);
+  Ordering expected2{X(0), X(1), X(2), X(3)};
+  EXPECT(assert_equal(expected2, actual));
+}
+
 /* ************************************************************************* */
 TEST(Ordering, AppendVector) {
   using symbol_shorthand::X;