From 456df093f110af74b6ee6e85ba6e44ced009a680 Mon Sep 17 00:00:00 2001
From: Fan Jiang <ProfFan@users.noreply.github.com>
Date: Mon, 2 Dec 2024 14:11:51 -0500
Subject: [PATCH] Change all occurances of unnamed enum (deprecated in C++20)
 to `constexpr`

---
 GTSAM-Concepts.md                        |  2 +-
 gtsam/base/GenericValue.h                |  3 +--
 gtsam/base/Lie.h                         |  4 ++--
 gtsam/base/Manifold.h                    |  4 ++--
 gtsam/base/Matrix.h                      |  2 +-
 gtsam/base/ProductLieGroup.h             |  6 +++---
 gtsam/base/VectorSpace.h                 | 10 +++++-----
 gtsam/basis/Basis.h                      |  2 +-
 gtsam/geometry/BearingRange.h            |  4 +---
 gtsam/geometry/Cal3.h                    |  2 +-
 gtsam/geometry/Cal3Bundler.h             |  2 +-
 gtsam/geometry/Cal3DS2.h                 |  2 +-
 gtsam/geometry/Cal3DS2_Base.h            |  2 +-
 gtsam/geometry/Cal3Fisheye.h             |  2 +-
 gtsam/geometry/Cal3Unified.h             |  2 +-
 gtsam/geometry/Cal3_S2.h                 |  2 +-
 gtsam/geometry/Cal3_S2Stereo.h           |  2 +-
 gtsam/geometry/Cal3f.h                   |  2 +-
 gtsam/geometry/CalibratedCamera.h        |  4 +---
 gtsam/geometry/EssentialMatrix.h         |  2 +-
 gtsam/geometry/FundamentalMatrix.h       |  4 ++--
 gtsam/geometry/Line3.h                   |  2 +-
 gtsam/geometry/OrientedPlane3.h          |  4 +---
 gtsam/geometry/PinholeCamera.h           |  4 +---
 gtsam/geometry/PinholePose.h             |  4 +---
 gtsam/geometry/Quaternion.h              |  4 +---
 gtsam/geometry/SOn.h                     |  2 +-
 gtsam/geometry/SphericalCamera.h         |  4 ++--
 gtsam/geometry/StereoCamera.h            |  4 +---
 gtsam/geometry/StereoPoint2.h            |  2 +-
 gtsam/geometry/Unit3.h                   |  4 +---
 gtsam/navigation/NavState.h              |  4 +---
 gtsam/nonlinear/ExpressionFactor.h       |  6 +++---
 gtsam/nonlinear/NonlinearFactor.h        |  2 +-
 gtsam/nonlinear/PriorFactor.h            |  2 +-
 gtsam/nonlinear/tests/testExpression.cpp |  2 +-
 gtsam/nonlinear/tests/testValues.cpp     |  2 +-
 gtsam/slam/BetweenFactor.h               |  8 ++++----
 gtsam/slam/FrobeniusFactor.h             |  6 +++---
 gtsam/slam/KarcherMeanFactor.h           |  2 +-
 gtsam_unstable/geometry/Event.h          |  2 +-
 41 files changed, 58 insertions(+), 77 deletions(-)

diff --git a/GTSAM-Concepts.md b/GTSAM-Concepts.md
index 9911b37649..733672fbe2 100644
--- a/GTSAM-Concepts.md
+++ b/GTSAM-Concepts.md
@@ -22,7 +22,7 @@ In GTSAM, all properties and operations needed to use a type must be defined thr
 In detail, we ask that the following items are defined in the traits object (although, not all are needed for optimization):
 
 * values:
-   * `enum { dimension = D};`, an enum that indicates the dimensionality *n* of the manifold. In Eigen-fashion, we also support manifolds whose dimensionality is only defined at runtime, by specifying the value -1.
+   * `inline constexpr static auto dimension = D;`, a constexpr that indicates the dimensionality *n* of the manifold. In Eigen-fashion, we also support manifolds whose dimensionality is only defined at runtime, by specifying the value -1.
 * types:
     * `TangentVector`, type that lives in tangent space. This will almost always be an `Eigen::Matrix<double,n,1>`.
     * `ChartJacobian`, a typedef for `OptionalJacobian<dimension, dimension>`.
diff --git a/gtsam/base/GenericValue.h b/gtsam/base/GenericValue.h
index bb92b6b2ee..87ce7a73d5 100644
--- a/gtsam/base/GenericValue.h
+++ b/gtsam/base/GenericValue.h
@@ -184,9 +184,8 @@ class GenericValue: public Value {
 	}
 #endif
 
-
   // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
-  enum { NeedsToAlign = (sizeof(T) % 16) == 0 };
+  constexpr static const bool NeedsToAlign = (sizeof(T) % 16) == 0;
 public:
   GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
 };
diff --git a/gtsam/base/Lie.h b/gtsam/base/Lie.h
index ce021e10eb..862ae6f4db 100644
--- a/gtsam/base/Lie.h
+++ b/gtsam/base/Lie.h
@@ -36,7 +36,7 @@ namespace gtsam {
 template <class Class, int N>
 struct LieGroup {
 
-  enum { dimension = N };
+  inline constexpr static auto dimension = N;
   typedef OptionalJacobian<N, N> ChartJacobian;
   typedef Eigen::Matrix<double, N, N> Jacobian;
   typedef Eigen::Matrix<double, N, 1> TangentVector;
@@ -183,7 +183,7 @@ struct LieGroupTraits: GetDimensionImpl<Class, Class::dimension> {
   /// @name Manifold
   /// @{
   typedef Class ManifoldType;
-  enum { dimension = Class::dimension };
+  inline constexpr static auto dimension = Class::dimension;
   typedef Eigen::Matrix<double, dimension, 1> TangentVector;
   typedef OptionalJacobian<dimension, dimension> ChartJacobian;
 
diff --git a/gtsam/base/Manifold.h b/gtsam/base/Manifold.h
index cb30fa9c01..922b8dd2f3 100644
--- a/gtsam/base/Manifold.h
+++ b/gtsam/base/Manifold.h
@@ -55,7 +55,7 @@ namespace internal {
 template<class Class>
 struct HasManifoldPrereqs {
 
-  enum { dim = Class::dimension };
+  inline constexpr static auto dim = Class::dimension;
 
   Class p, q;
   Eigen::Matrix<double, dim, 1> v;
@@ -95,7 +95,7 @@ struct ManifoldTraits: GetDimensionImpl<Class, Class::dimension> {
   GTSAM_CONCEPT_ASSERT(HasManifoldPrereqs<Class>);
 
   // Dimension of the manifold
-  enum { dimension = Class::dimension };
+  inline constexpr static auto dimension = Class::dimension;
 
   // Typedefs required by all manifold types.
   typedef Class ManifoldType;
diff --git a/gtsam/base/Matrix.h b/gtsam/base/Matrix.h
index 6dba9cb051..c8dc46ed51 100644
--- a/gtsam/base/Matrix.h
+++ b/gtsam/base/Matrix.h
@@ -479,7 +479,7 @@ struct MultiplyWithInverse {
  */
 template <typename T, int N>
 struct MultiplyWithInverseFunction {
-  enum { M = traits<T>::dimension };
+  inline constexpr static auto M = traits<T>::dimension;
   typedef Eigen::Matrix<double, N, 1> VectorN;
   typedef Eigen::Matrix<double, N, N> MatrixN;
 
diff --git a/gtsam/base/ProductLieGroup.h b/gtsam/base/ProductLieGroup.h
index 085da712a8..bb7ba72b88 100644
--- a/gtsam/base/ProductLieGroup.h
+++ b/gtsam/base/ProductLieGroup.h
@@ -67,9 +67,9 @@ class ProductLieGroup: public std::pair<G, H> {
 
   /// @name Manifold
   /// @{
-  enum {dimension = dimension1 + dimension2};
-  inline static size_t Dim() {return dimension;}
-  inline size_t dim() const {return dimension;}
+  inline constexpr static auto dimension = dimension1 + dimension2;
+  inline static size_t Dim() { return dimension; }
+  inline size_t dim() const { return dimension; }
 
   typedef Eigen::Matrix<double, dimension, 1> TangentVector;
   typedef OptionalJacobian<dimension, dimension> ChartJacobian;
diff --git a/gtsam/base/VectorSpace.h b/gtsam/base/VectorSpace.h
index a9e9ca1065..c5c4ad622b 100644
--- a/gtsam/base/VectorSpace.h
+++ b/gtsam/base/VectorSpace.h
@@ -163,7 +163,7 @@ struct VectorSpaceImpl<Class,Eigen::Dynamic> {
 template<class Class>
 struct HasVectorSpacePrereqs {
 
-  enum { dim = Class::dimension };
+  inline constexpr static auto dim = Class::dimension;
 
   Class p, q;
   Vector v;
@@ -197,7 +197,7 @@ GTSAM_CONCEPT_ASSERT(HasVectorSpacePrereqs<Class>);
 
   /// @name Manifold
   /// @{
-  enum { dimension = Class::dimension};
+  inline constexpr static auto dimension = Class::dimension;
   typedef Class ManifoldType;
   /// @}
 };
@@ -232,7 +232,7 @@ struct ScalarTraits : VectorSpaceImpl<Scalar, 1> {
   /// @name Manifold
   /// @{
   typedef Scalar ManifoldType;
-  enum { dimension = 1 };
+  inline constexpr static auto dimension = 1;
   typedef Eigen::Matrix<double, 1, 1> TangentVector;
   typedef OptionalJacobian<1, 1> ChartJacobian;
 
@@ -305,7 +305,7 @@ struct traits<Eigen::Matrix<double, M, N, Options, MaxRows, MaxCols> > :
 
   /// @name Manifold
   /// @{
-  enum { dimension = M*N};
+  inline constexpr static auto dimension = M * N;
   typedef Fixed ManifoldType;
   typedef Eigen::Matrix<double, dimension, 1> TangentVector;
   typedef Eigen::Matrix<double, dimension, dimension> Jacobian;
@@ -377,7 +377,7 @@ struct DynamicTraits {
 
   /// @name Manifold
   /// @{
-  enum { dimension = Eigen::Dynamic };
+  inline constexpr static auto dimension = Eigen::Dynamic;
   typedef Eigen::VectorXd TangentVector;
   typedef Eigen::MatrixXd Jacobian;
   typedef OptionalJacobian<dimension, dimension> ChartJacobian;
diff --git a/gtsam/basis/Basis.h b/gtsam/basis/Basis.h
index 1b1c44acc0..960440daf2 100644
--- a/gtsam/basis/Basis.h
+++ b/gtsam/basis/Basis.h
@@ -291,7 +291,7 @@ class Basis {
    */
   template <class T>
   class ManifoldEvaluationFunctor : public VectorEvaluationFunctor {
-    enum { M = traits<T>::dimension };
+    inline constexpr static auto M = traits<T>::dimension;
     using Base = VectorEvaluationFunctor;
 
    public:
diff --git a/gtsam/geometry/BearingRange.h b/gtsam/geometry/BearingRange.h
index 9b8fe1f875..07229dfcae 100644
--- a/gtsam/geometry/BearingRange.h
+++ b/gtsam/geometry/BearingRange.h
@@ -162,9 +162,7 @@ struct BearingRange {
   /// @}
 
   // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
-  enum {
-    NeedsToAlign = (sizeof(B) % 16) == 0 || (sizeof(R) % 16) == 0
-  };
+  inline constexpr static auto NeedsToAlign = (sizeof(B) % 16) == 0 || (sizeof(R) % 16) == 0;
 public:
   GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
 };
diff --git a/gtsam/geometry/Cal3.h b/gtsam/geometry/Cal3.h
index 1b66eb3363..5eecee8451 100644
--- a/gtsam/geometry/Cal3.h
+++ b/gtsam/geometry/Cal3.h
@@ -73,7 +73,7 @@ class GTSAM_EXPORT Cal3 {
   double u0_ = 0.0f, v0_ = 0.0f;  ///< principal point
 
  public:
-  enum { dimension = 5 };
+  inline constexpr static auto dimension = 5;
   ///< shared pointer to calibration object
   using shared_ptr = std::shared_ptr<Cal3>;
 
diff --git a/gtsam/geometry/Cal3Bundler.h b/gtsam/geometry/Cal3Bundler.h
index 081688d48c..01eb9437ac 100644
--- a/gtsam/geometry/Cal3Bundler.h
+++ b/gtsam/geometry/Cal3Bundler.h
@@ -37,7 +37,7 @@ class GTSAM_EXPORT Cal3Bundler : public Cal3f {
   // Note: u0 and v0 are constants and not optimized.
 
  public:
-  enum { dimension = 3 };
+  inline constexpr static auto dimension = 3;
   using shared_ptr = std::shared_ptr<Cal3Bundler>;
 
   /// @name Constructors
diff --git a/gtsam/geometry/Cal3DS2.h b/gtsam/geometry/Cal3DS2.h
index a7ca08afcc..0ecfc24aef 100644
--- a/gtsam/geometry/Cal3DS2.h
+++ b/gtsam/geometry/Cal3DS2.h
@@ -36,7 +36,7 @@ class GTSAM_EXPORT Cal3DS2 : public Cal3DS2_Base {
   using Base = Cal3DS2_Base;
 
  public:
-  enum { dimension = 9 };
+  inline constexpr static auto dimension = 9;
 
   ///< shared pointer to stereo calibration object
   using shared_ptr = std::shared_ptr<Cal3DS2>;
diff --git a/gtsam/geometry/Cal3DS2_Base.h b/gtsam/geometry/Cal3DS2_Base.h
index b0ef0368b5..6eff04c101 100644
--- a/gtsam/geometry/Cal3DS2_Base.h
+++ b/gtsam/geometry/Cal3DS2_Base.h
@@ -46,7 +46,7 @@ class GTSAM_EXPORT Cal3DS2_Base : public Cal3 {
   double tol_ = 1e-5;             ///< tolerance value when calibrating
 
  public:
-  enum { dimension = 9 };
+  inline constexpr static auto dimension = 9;
 
   ///< shared pointer to stereo calibration object
   using shared_ptr = std::shared_ptr<Cal3DS2_Base>;
diff --git a/gtsam/geometry/Cal3Fisheye.h b/gtsam/geometry/Cal3Fisheye.h
index 3f1cac148f..4c542c5bea 100644
--- a/gtsam/geometry/Cal3Fisheye.h
+++ b/gtsam/geometry/Cal3Fisheye.h
@@ -55,7 +55,7 @@ class GTSAM_EXPORT Cal3Fisheye : public Cal3 {
   double tol_ = 1e-5;             ///< tolerance value when calibrating
 
  public:
-  enum { dimension = 9 };
+  inline constexpr static auto dimension = 9;
   ///< shared pointer to fisheye calibration object
   using shared_ptr = std::shared_ptr<Cal3Fisheye>;
 
diff --git a/gtsam/geometry/Cal3Unified.h b/gtsam/geometry/Cal3Unified.h
index 309b6dca1d..7eb4d2edba 100644
--- a/gtsam/geometry/Cal3Unified.h
+++ b/gtsam/geometry/Cal3Unified.h
@@ -50,7 +50,7 @@ class GTSAM_EXPORT Cal3Unified : public Cal3DS2_Base {
   double xi_ = 0.0f;  ///< mirror parameter
 
  public:
-  enum { dimension = 10 };
+  inline constexpr static auto dimension = 10;
 
   ///< shared pointer to stereo calibration object
   using shared_ptr = std::shared_ptr<Cal3Unified>;
diff --git a/gtsam/geometry/Cal3_S2.h b/gtsam/geometry/Cal3_S2.h
index 885be614f7..568cde41eb 100644
--- a/gtsam/geometry/Cal3_S2.h
+++ b/gtsam/geometry/Cal3_S2.h
@@ -33,7 +33,7 @@ namespace gtsam {
  */
 class GTSAM_EXPORT Cal3_S2 : public Cal3 {
  public:
-  enum { dimension = 5 };
+  inline constexpr static auto dimension = 5;
 
   ///< shared pointer to calibration object
   using shared_ptr = std::shared_ptr<Cal3_S2>;
diff --git a/gtsam/geometry/Cal3_S2Stereo.h b/gtsam/geometry/Cal3_S2Stereo.h
index 4fee1a0220..292519cfd8 100644
--- a/gtsam/geometry/Cal3_S2Stereo.h
+++ b/gtsam/geometry/Cal3_S2Stereo.h
@@ -32,7 +32,7 @@ class GTSAM_EXPORT Cal3_S2Stereo : public Cal3_S2 {
   double b_ = 1.0f;  ///< Stereo baseline.
 
  public:
-  enum { dimension = 6 };
+  inline constexpr static auto dimension = 6;
 
   ///< shared pointer to stereo calibration object
   using shared_ptr = std::shared_ptr<Cal3_S2Stereo>;
diff --git a/gtsam/geometry/Cal3f.h b/gtsam/geometry/Cal3f.h
index f053f3d112..6c3c214b8b 100644
--- a/gtsam/geometry/Cal3f.h
+++ b/gtsam/geometry/Cal3f.h
@@ -34,7 +34,7 @@ namespace gtsam {
  */
 class GTSAM_EXPORT Cal3f : public Cal3 {
  public:
-  enum { dimension = 1 };
+  inline constexpr static auto dimension = 1;
   using shared_ptr = std::shared_ptr<Cal3f>;
 
   /// @name Constructors
diff --git a/gtsam/geometry/CalibratedCamera.h b/gtsam/geometry/CalibratedCamera.h
index dca15feb2c..d3d1e1b9a2 100644
--- a/gtsam/geometry/CalibratedCamera.h
+++ b/gtsam/geometry/CalibratedCamera.h
@@ -252,9 +252,7 @@ class GTSAM_EXPORT CalibratedCamera: public PinholeBase {
 
 public:
 
-  enum {
-    dimension = 6
-  };
+  inline constexpr static auto dimension = 6;
 
   /// @name Standard Constructors
   /// @{
diff --git a/gtsam/geometry/EssentialMatrix.h b/gtsam/geometry/EssentialMatrix.h
index d514c4f195..3986f30631 100644
--- a/gtsam/geometry/EssentialMatrix.h
+++ b/gtsam/geometry/EssentialMatrix.h
@@ -82,7 +82,7 @@ class EssentialMatrix {
 
   /// @name Manifold
   /// @{
-  enum { dimension = 5 };
+  inline constexpr static auto dimension = 5;
   inline static size_t Dim() { return dimension;}
   inline size_t dim() const { return dimension;}
 
diff --git a/gtsam/geometry/FundamentalMatrix.h b/gtsam/geometry/FundamentalMatrix.h
index df2c2881af..0752ced7d7 100644
--- a/gtsam/geometry/FundamentalMatrix.h
+++ b/gtsam/geometry/FundamentalMatrix.h
@@ -102,7 +102,7 @@ class GTSAM_EXPORT FundamentalMatrix {
 
   /// @name Manifold
   /// @{
-  enum { dimension = 7 };  // 3 for U, 1 for s, 3 for V
+  inline constexpr static auto dimension = 7;  // 3 for U, 1 for s, 3 for V
   inline static size_t Dim() { return dimension; }
   inline size_t dim() const { return dimension; }
 
@@ -179,7 +179,7 @@ class GTSAM_EXPORT SimpleFundamentalMatrix {
 
   /// @name Manifold
   /// @{
-  enum { dimension = 7 };  // 5 for E, 1 for fa, 1 for fb
+  inline constexpr static auto dimension = 7;  // 5 for E, 1 for fa, 1 for fb
   inline static size_t Dim() { return dimension; }
   inline size_t dim() const { return dimension; }
 
diff --git a/gtsam/geometry/Line3.h b/gtsam/geometry/Line3.h
index def49d2682..5ae50e138e 100644
--- a/gtsam/geometry/Line3.h
+++ b/gtsam/geometry/Line3.h
@@ -47,7 +47,7 @@ class GTSAM_EXPORT Line3 {
   double a_, b_;  // Intersection of line with the world x-y plane rotated by R_
   // Also the closest point on line to origin
  public:
-  enum { dimension = 4 };
+  inline constexpr static auto dimension = 4;
 
   /** Default constructor is the Z axis **/
   Line3() :
diff --git a/gtsam/geometry/OrientedPlane3.h b/gtsam/geometry/OrientedPlane3.h
index 07c8445fe8..3d84086ac4 100644
--- a/gtsam/geometry/OrientedPlane3.h
+++ b/gtsam/geometry/OrientedPlane3.h
@@ -39,9 +39,7 @@ class GTSAM_EXPORT OrientedPlane3 {
   double d_;    ///< The perpendicular distance to this plane
 
 public:
-  enum {
-    dimension = 3
-  };
+  inline constexpr static auto dimension = 3;
 
   /// @name Constructors
   /// @{
diff --git a/gtsam/geometry/PinholeCamera.h b/gtsam/geometry/PinholeCamera.h
index 8329664fdf..0439b2fde7 100644
--- a/gtsam/geometry/PinholeCamera.h
+++ b/gtsam/geometry/PinholeCamera.h
@@ -51,9 +51,7 @@ class PinholeCamera: public PinholeBaseK<Calibration> {
 
 public:
 
-  enum {
-    dimension = 6 + DimK
-  }; ///< Dimension depends on calibration
+  inline constexpr static auto dimension = 6 + DimK; ///< Dimension depends on calibration
 
   /// @name Standard Constructors
   /// @{
diff --git a/gtsam/geometry/PinholePose.h b/gtsam/geometry/PinholePose.h
index df6ec5c08a..f1191dbcc4 100644
--- a/gtsam/geometry/PinholePose.h
+++ b/gtsam/geometry/PinholePose.h
@@ -245,9 +245,7 @@ class PinholePose: public PinholeBaseK<CALIBRATION> {
 
 public:
 
-  enum {
-    dimension = 6
-  }; ///< There are 6 DOF to optimize for
+  inline constexpr static auto dimension = 6; ///< There are 6 DOF to optimize for
 
   /// @name Standard Constructors
   /// @{
diff --git a/gtsam/geometry/Quaternion.h b/gtsam/geometry/Quaternion.h
index f9ed2a383e..36f8915051 100644
--- a/gtsam/geometry/Quaternion.h
+++ b/gtsam/geometry/Quaternion.h
@@ -45,9 +45,7 @@ struct traits<QUATERNION_TYPE> {
   /// @}
   /// @name Basic manifold traits
   /// @{
-  enum {
-    dimension = 3
-  };
+  inline constexpr static auto dimension = 3;
   typedef OptionalJacobian<3, 3> ChartJacobian;
   typedef Eigen::Matrix<_Scalar, 3, 1, _Options, 3, 1> TangentVector;
 
diff --git a/gtsam/geometry/SOn.h b/gtsam/geometry/SOn.h
index 75ff872a8e..b0da3b213d 100644
--- a/gtsam/geometry/SOn.h
+++ b/gtsam/geometry/SOn.h
@@ -54,7 +54,7 @@ constexpr int NSquaredSO(int N) { return (N < 0) ? Eigen::Dynamic : N * N; }
 template <int N>
 class SO : public LieGroup<SO<N>, internal::DimensionSO(N)> {
  public:
-  enum { dimension = internal::DimensionSO(N) };
+  inline constexpr static auto dimension = internal::DimensionSO(N);
   using MatrixNN = Eigen::Matrix<double, N, N>;
   using VectorN2 = Eigen::Matrix<double, internal::NSquaredSO(N), 1>;
   using MatrixDD = Eigen::Matrix<double, dimension, dimension>;
diff --git a/gtsam/geometry/SphericalCamera.h b/gtsam/geometry/SphericalCamera.h
index ef20aa7fe7..1ff87cec3a 100644
--- a/gtsam/geometry/SphericalCamera.h
+++ b/gtsam/geometry/SphericalCamera.h
@@ -41,7 +41,7 @@ namespace gtsam {
  */
 class GTSAM_EXPORT EmptyCal {
  public:
-  enum { dimension = 0 };
+  inline constexpr static auto dimension = 0;
   EmptyCal() {}
   virtual ~EmptyCal() = default;
   using shared_ptr = std::shared_ptr<EmptyCal>;
@@ -73,7 +73,7 @@ class GTSAM_EXPORT EmptyCal {
  */
 class GTSAM_EXPORT SphericalCamera {
  public:
-  enum { dimension = 6 };
+  inline constexpr static auto dimension = 6;
 
   using Measurement = Unit3;
   using MeasurementVector = std::vector<Unit3>;
diff --git a/gtsam/geometry/StereoCamera.h b/gtsam/geometry/StereoCamera.h
index da71dd0707..026125572b 100644
--- a/gtsam/geometry/StereoCamera.h
+++ b/gtsam/geometry/StereoCamera.h
@@ -61,9 +61,7 @@ class GTSAM_EXPORT StereoCamera {
 
 public:
 
-  enum {
-    dimension = 6
-  };
+  inline constexpr static auto dimension = 6;
 
   /// @name Standard Constructors
   /// @{
diff --git a/gtsam/geometry/StereoPoint2.h b/gtsam/geometry/StereoPoint2.h
index 4383e212e4..7a1910e42e 100644
--- a/gtsam/geometry/StereoPoint2.h
+++ b/gtsam/geometry/StereoPoint2.h
@@ -37,7 +37,7 @@ class GTSAM_EXPORT StereoPoint2 {
   double uL_, uR_, v_;
 
 public:
-  enum { dimension = 3 };
+  inline constexpr static auto dimension = 3;
   /// @name Standard Constructors
   /// @{
 
diff --git a/gtsam/geometry/Unit3.h b/gtsam/geometry/Unit3.h
index 18bc5d9f04..a7304280f2 100644
--- a/gtsam/geometry/Unit3.h
+++ b/gtsam/geometry/Unit3.h
@@ -53,9 +53,7 @@ class GTSAM_EXPORT Unit3 {
 
 public:
 
-  enum {
-    dimension = 2
-  };
+  inline constexpr static auto dimension = 2;
 
   /// @name Constructors
   /// @{
diff --git a/gtsam/navigation/NavState.h b/gtsam/navigation/NavState.h
index f778a71231..35ce435a37 100644
--- a/gtsam/navigation/NavState.h
+++ b/gtsam/navigation/NavState.h
@@ -42,9 +42,7 @@ class GTSAM_EXPORT NavState {
 
 public:
 
-  enum {
-    dimension = 9
-  };
+  inline constexpr static auto dimension = 9;
 
   typedef std::pair<Point3, Velocity3> PositionAndVelocity;
 
diff --git a/gtsam/nonlinear/ExpressionFactor.h b/gtsam/nonlinear/ExpressionFactor.h
index b3e34d079e..d9af1933c6 100644
--- a/gtsam/nonlinear/ExpressionFactor.h
+++ b/gtsam/nonlinear/ExpressionFactor.h
@@ -224,9 +224,9 @@ class ExpressionFactor : public NoiseModelFactor {
 #endif
 
  // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
- enum { NeedsToAlign = (sizeof(T) % 16) == 0 };
-  public:
-	  GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
+ inline constexpr static auto NeedsToAlign = (sizeof(T) % 16) == 0;
+ public:
+  GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
 };
 // ExpressionFactor
 
diff --git a/gtsam/nonlinear/NonlinearFactor.h b/gtsam/nonlinear/NonlinearFactor.h
index 2d3a13766e..101743b783 100644
--- a/gtsam/nonlinear/NonlinearFactor.h
+++ b/gtsam/nonlinear/NonlinearFactor.h
@@ -434,7 +434,7 @@ class NoiseModelFactorN
       public detail::NoiseModelFactorAliases<ValueTypes...> {
  public:
   /// N is the number of variables (N-way factor)
-  enum { N = sizeof...(ValueTypes) };
+  inline constexpr static auto N = sizeof...(ValueTypes);
 
   using NoiseModelFactor::unwhitenedError;
 
diff --git a/gtsam/nonlinear/PriorFactor.h b/gtsam/nonlinear/PriorFactor.h
index ab2a66a77a..1593734590 100644
--- a/gtsam/nonlinear/PriorFactor.h
+++ b/gtsam/nonlinear/PriorFactor.h
@@ -118,7 +118,7 @@ namespace gtsam {
 #endif
 
   // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
-  enum { NeedsToAlign = (sizeof(T) % 16) == 0 };
+  inline constexpr static auto NeedsToAlign = (sizeof(T) % 16) == 0;
   public:
   GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
   };
diff --git a/gtsam/nonlinear/tests/testExpression.cpp b/gtsam/nonlinear/tests/testExpression.cpp
index 6f5fc53f58..67815e262d 100644
--- a/gtsam/nonlinear/tests/testExpression.cpp
+++ b/gtsam/nonlinear/tests/testExpression.cpp
@@ -115,7 +115,7 @@ TEST(Expression, Unary3) {
 // Simple test class that implements the `VectorSpace` protocol.
 class Class : public Point3 {
  public:
-  enum {dimension = 3};
+  inline constexpr static auto dimension = 3;
   using Point3::Point3;
   const Vector3& vector() const { return *this; }
   inline static Class Identity() { return Class(0,0,0); }
diff --git a/gtsam/nonlinear/tests/testValues.cpp b/gtsam/nonlinear/tests/testValues.cpp
index a2b265a56f..06eb46d4c1 100644
--- a/gtsam/nonlinear/tests/testValues.cpp
+++ b/gtsam/nonlinear/tests/testValues.cpp
@@ -54,7 +54,7 @@ int TestValueData::DestructorCount = 0;
 class TestValue {
   TestValueData data_;
 public:
-  enum {dimension = 0};
+  inline constexpr static auto dimension = 0;
   void print(const std::string& str = "") const {}
   bool equals(const TestValue& other, double tol = 1e-9) const { return true; }
   size_t dim() const { return 0; }
diff --git a/gtsam/slam/BetweenFactor.h b/gtsam/slam/BetweenFactor.h
index 6eaa5c01b8..3e2478e739 100644
--- a/gtsam/slam/BetweenFactor.h
+++ b/gtsam/slam/BetweenFactor.h
@@ -147,10 +147,10 @@ namespace gtsam {
     }
 #endif
 
-	  // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
-	  enum { NeedsToAlign = (sizeof(VALUE) % 16) == 0 };
-    public:
-      GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
+    // Alignment, see https://eigen.tuxfamily.org/dox/group__TopicStructHavingEigenMembers.html
+    inline constexpr static auto NeedsToAlign = (sizeof(VALUE) % 16) == 0;
+  public:
+    GTSAM_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)
   }; // \class BetweenFactor
 
   /// traits
diff --git a/gtsam/slam/FrobeniusFactor.h b/gtsam/slam/FrobeniusFactor.h
index a000a15140..37efa5f24b 100644
--- a/gtsam/slam/FrobeniusFactor.h
+++ b/gtsam/slam/FrobeniusFactor.h
@@ -49,7 +49,7 @@ ConvertNoiseModel(const SharedNoiseModel &model, size_t n,
  */
 template <class Rot>
 class FrobeniusPrior : public NoiseModelFactorN<Rot> {
-  enum { Dim = Rot::VectorN2::RowsAtCompileTime };
+  inline constexpr static auto Dim = Rot::VectorN2::RowsAtCompileTime;
   using MatrixNN = typename Rot::MatrixNN;
   Eigen::Matrix<double, Dim, 1> vecM_;  ///< vectorized matrix to approximate
 
@@ -79,7 +79,7 @@ class FrobeniusPrior : public NoiseModelFactorN<Rot> {
  */
 template <class Rot>
 class FrobeniusFactor : public NoiseModelFactorN<Rot, Rot> {
-  enum { Dim = Rot::VectorN2::RowsAtCompileTime };
+  inline constexpr static auto Dim = Rot::VectorN2::RowsAtCompileTime;
 
  public:
 
@@ -111,7 +111,7 @@ class FrobeniusBetweenFactor : public NoiseModelFactorN<Rot, Rot> {
   Rot R12_;  ///< measured rotation between R1 and R2
   Eigen::Matrix<double, Rot::dimension, Rot::dimension>
       R2hat_H_R1_;  ///< fixed derivative of R2hat wrpt R1
-  enum { Dim = Rot::VectorN2::RowsAtCompileTime };
+  inline constexpr static auto Dim = Rot::VectorN2::RowsAtCompileTime;
 
  public:
 
diff --git a/gtsam/slam/KarcherMeanFactor.h b/gtsam/slam/KarcherMeanFactor.h
index 4e82ca1d96..6b25dd261f 100644
--- a/gtsam/slam/KarcherMeanFactor.h
+++ b/gtsam/slam/KarcherMeanFactor.h
@@ -45,7 +45,7 @@ template <class T> T FindKarcherMean(std::initializer_list<T> &&rotations);
  * */
 template <class T> class KarcherMeanFactor : public NonlinearFactor {
   // Compile time dimension: can be -1
-  enum { D = traits<T>::dimension };
+  inline constexpr static auto D = traits<T>::dimension;
 
   // Runtime dimension: always >=0
   size_t d_;
diff --git a/gtsam_unstable/geometry/Event.h b/gtsam_unstable/geometry/Event.h
index a3c9076462..471ada35b3 100644
--- a/gtsam_unstable/geometry/Event.h
+++ b/gtsam_unstable/geometry/Event.h
@@ -39,7 +39,7 @@ class GTSAM_UNSTABLE_EXPORT Event {
   Point3 location_;  ///< Location at time event was generated
 
  public:
-  enum { dimension = 4 };
+  inline constexpr static auto dimension = 4;
 
   /// Default Constructor
   Event() : time_(0), location_(0, 0, 0) {}