Eigen check for get_member to avoid invocable branch (#1458)

Author: stephenberry

include/glaze/concepts/container_concepts.hpp

@@ -220,6 +220,21 @@ namespace glz
       requires !std::same_as<void, decltype(t.end())>;
       requires std::input_iterator<decltype(t.begin())>;
    };
+   
+   template <class T>
+   concept matrix_t = requires(T matrix) {
+      matrix.resize(2, 4);
+      matrix.data();
+      {
+         matrix.rows()
+      } -> std::convertible_to<size_t>;
+      {
+         matrix.cols()
+      } -> std::convertible_to<size_t>;
+      {
+         matrix.size()
+      } -> std::convertible_to<size_t>;
+   } && !range<T>;
 
    // range like
    template <class T>

include/glaze/core/common.hpp

@@ -422,7 +422,10 @@ namespace glz
          else if constexpr (std::is_member_function_pointer_v<V>) {
             return element;
          }
-         else if constexpr (std::invocable<Element, Value>) {
+         else if constexpr (std::invocable<Element, Value> && not matrix_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()()
             return std::invoke(std::forward<Element>(element), std::forward<Value>(value));
          }
          else if constexpr (std::is_pointer_v<V>) {

include/glaze/ext/eigen.hpp

@@ -24,21 +24,6 @@ namespace glz
 {
    namespace detail
    {
-      template <class T>
-      concept matrix_t = requires(T matrix) {
-         matrix.resize(2, 4);
-         matrix.data();
-         {
-            matrix.rows()
-         } -> std::convertible_to<size_t>;
-         {
-            matrix.cols()
-         } -> std::convertible_to<size_t>;
-         {
-            matrix.size()
-         } -> std::convertible_to<size_t>;
-      } && !range<T>;
-
       template <matrix_t T>
          requires(T::RowsAtCompileTime >= 0 && T::ColsAtCompileTime >= 0)
       struct from<BEVE, T>

tests/eigen_test/eigen_test.cpp

@@ -19,9 +19,28 @@
 #include "glaze/json/write.hpp"
 #include "ut/ut.hpp"
 
+using namespace ut;
+
+struct test_struct
+{
+  Eigen::Matrix3d d = Eigen::Matrix3d::Identity();
+} test_value;
+
+suite matrix3d = [] {
+   "eigen Matrix3d"_test = [] {
+      auto result = glz::write_json(test_value.d).value();
+      expect(result == "[1,0,0,0,1,0,0,0,1]") << result;
+      
+      static_assert(glz::reflect<test_struct>::size == 1);
+      static_assert(glz::reflect<test_struct>::keys[0] == "d");
+      
+      result = glz::write_json(test_value).value();
+      expect(result == R"({"d":[1,0,0,0,1,0,0,0,1]})") << result;
+   };
+};
+
 int main()
 {
-   using namespace ut;
    "write_json"_test = [] {
       Eigen::Matrix<double, 2, 2> m{};
       m << 5, 1, 1, 7;