From 4cc2e22b59515767f79d41934c99749116521fa0 Mon Sep 17 00:00:00 2001
From: Frank Dellaert <dellaert@gmail.com>
Date: Tue, 29 Apr 2025 00:20:04 -0400
Subject: [PATCH] Add value to concepts

---
 gtsam/base/Lie.h      | 6 +++++-
 gtsam/base/Manifold.h | 5 ++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/gtsam/base/Lie.h b/gtsam/base/Lie.h
index 5b3173b37..4248f16b2 100644
--- a/gtsam/base/Lie.h
+++ b/gtsam/base/Lie.h
@@ -277,6 +277,10 @@ inline Class expmap_default(const Class& t, const Vector& d) {
 template<typename T>
 class IsLieGroup: public IsGroup<T>, public IsManifold<T> {
 public:
+  // Concept marker: allows checking IsLieGroup<T>::value in templates
+  static constexpr bool value =
+    std::is_base_of<lie_group_tag, typename traits<T>::structure_category>::value;
+
   typedef typename traits<T>::structure_category structure_category_tag;
   typedef typename traits<T>::ManifoldType ManifoldType;
   typedef typename traits<T>::TangentVector TangentVector;
@@ -284,7 +288,7 @@ public:
 
   GTSAM_CONCEPT_USAGE(IsLieGroup) {
     static_assert(
-        (std::is_base_of<lie_group_tag, structure_category_tag>::value),
+        value,
         "This type's trait does not assert it is a Lie group (or derived)");
 
     // group operations with Jacobians
diff --git a/gtsam/base/Manifold.h b/gtsam/base/Manifold.h
index 80a9cd166..18ae9b616 100644
--- a/gtsam/base/Manifold.h
+++ b/gtsam/base/Manifold.h
@@ -138,10 +138,13 @@ public:
   static const int dim = traits<T>::dimension;
   typedef typename traits<T>::ManifoldType ManifoldType;
   typedef typename traits<T>::TangentVector TangentVector;
+  // Concept marker: allows checking IsManifold<T>::value in templates
+  static constexpr bool value =
+    std::is_base_of<manifold_tag, structure_category_tag>::value;
 
   GTSAM_CONCEPT_USAGE(IsManifold) {
     static_assert(
-        (std::is_base_of<manifold_tag, structure_category_tag>::value),
+        value,
         "This type's structure_category trait does not assert it as a manifold (or derived)");
     static_assert(TangentVector::SizeAtCompileTime == dim);