From c0bc0d36b1b4770d72fcb313a68591432f75ae1f Mon Sep 17 00:00:00 2001
From: Stephen Berry <stephenberry.developer@gmail.com>
Date: Mon, 6 Jan 2025 09:21:05 -0600
Subject: [PATCH] Support for reflection with Eigen vector types (#1552)

---
 include/glaze/concepts/container_concepts.hpp | 22 ++++++++++++++++---
 include/glaze/core/common.hpp                 |  2 +-
 tests/eigen_test/eigen_test.cpp               |  8 ++-----
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/include/glaze/concepts/container_concepts.hpp b/include/glaze/concepts/container_concepts.hpp
index e8361d97d0..97e2faa1b4 100644
--- a/include/glaze/concepts/container_concepts.hpp
+++ b/include/glaze/concepts/container_concepts.hpp
@@ -265,20 +265,36 @@ namespace glz
       requires std::input_iterator<decltype(t.begin())>;
    };
 
+   // Concept for a matrix type (not a vector, which is a range)
    template <class T>
    concept matrix_t = requires(T matrix) {
       matrix.resize(2, 4);
       matrix.data();
       {
          matrix.rows()
-      } -> std::convertible_to<size_t>;
+      } -> std::convertible_to<int>;
       {
          matrix.cols()
-      } -> std::convertible_to<size_t>;
+      } -> std::convertible_to<int>;
       {
          matrix.size()
-      } -> std::convertible_to<size_t>;
+      } -> std::convertible_to<int>;
    } && !range<T>;
+   
+   // concept for the Eigen library: matrices and vectors
+   template <class T>
+   concept eigen_t = requires(T matrix) {
+      matrix.data();
+      {
+         matrix.rows()
+      } -> std::convertible_to<int>;
+      {
+         matrix.cols()
+      } -> std::convertible_to<int>;
+      {
+         matrix.size()
+      } -> std::convertible_to<int>;
+   };
 
    // range like
    template <class T>
diff --git a/include/glaze/core/common.hpp b/include/glaze/core/common.hpp
index 85aed58c97..038c2fd410 100644
--- a/include/glaze/core/common.hpp
+++ b/include/glaze/core/common.hpp
@@ -454,7 +454,7 @@ namespace glz
       else if constexpr (std::is_member_function_pointer_v<V>) {
          return element;
       }
-      else if constexpr (std::invocable<Element, Value> && not matrix_t<Element>) {
+      else if constexpr (std::invocable<Element, Value> && not eigen_t<Element>) {
          // Eigen places a static_assert inside of the operator()(), so we must target
          // matrix types and reject them from the invocable check
          // Eigen ought to put the check in the `enable_if` for operator()()
diff --git a/tests/eigen_test/eigen_test.cpp b/tests/eigen_test/eigen_test.cpp
index 473a51e9f6..8d8fbcaf9d 100644
--- a/tests/eigen_test/eigen_test.cpp
+++ b/tests/eigen_test/eigen_test.cpp
@@ -45,12 +45,8 @@ struct complex_struct
    Eigen::MatrixXcd mcd;
 } complex_test_value;
 
-template <>
-struct glz::meta<complex_struct>
-{
-   using T = complex_struct;
-   static constexpr auto value = object(&T::mf, &T::vi, &T::mcd);
-};
+static_assert(glz::eigen_t<Eigen::Matrix2f>);
+static_assert(glz::eigen_t<Eigen::Vector4i>);
 
 // Initialize complex_test_value
 void initialize_complex_struct()