diff --git a/g2o/core/abstract_graph.h b/g2o/core/abstract_graph.h
index 557472096..96d026a60 100644
--- a/g2o/core/abstract_graph.h
+++ b/g2o/core/abstract_graph.h
@@ -109,30 +109,51 @@ class G2O_CORE_API AbstractGraph {
   AbstractGraph() = default;
   ~AbstractGraph() = default;
 
+  /**
+   * @brief Load from the input assuming given format
+   *
+   * @param input The input stream for reading data.
+   * @param format The output format.
+   * @return true iff loading was successful
+   */
   bool load(std::istream& input, io::Format format);
 
   [[nodiscard]] bool save(std::ostream& output, io::Format format) const;
 
+  //! The ids of fixed vertices
   std::vector<int>& fixed() { return fixed_; };
   [[nodiscard]] const std::vector<int>& fixed() const { return fixed_; };
 
+  //! The parameters of the graph
   std::vector<AbstractParameter>& parameters() { return parameters_; };
   [[nodiscard]] const std::vector<AbstractParameter>& parameters() const {
     return parameters_;
   };
 
+  //! The vertices of the graph
   std::vector<AbstractVertex>& vertices() { return vertices_; };
   [[nodiscard]] const std::vector<AbstractVertex>& vertices() const {
     return vertices_;
   };
 
+  //! The edges of the graph
   std::vector<AbstractEdge>& edges() { return edges_; };
   [[nodiscard]] const std::vector<AbstractEdge>& edges() const {
     return edges_;
   };
 
+  /**
+   * @brief Clear all structures of the graph.
+   *
+   * Clear all vertices, edges, and parameters of the graph.
+   */
   void clear();
 
+  /**
+   * @brief Set a mapping for renaming tags.
+   *
+   * @param tag_mapping mapping from -> to for renaming types in the graph.
+   */
   void renameTags(
       const std::unordered_map<std::string, std::string>& tag_mapping);
 
diff --git a/g2o/core/io/io_g2o.cpp b/g2o/core/io/io_g2o.cpp
index b6d89f717..98eff3698 100644
--- a/g2o/core/io/io_g2o.cpp
+++ b/g2o/core/io/io_g2o.cpp
@@ -29,6 +29,7 @@
 #include <iostream>
 #include <sstream>
 #include <string>
+#include <type_traits>
 #include <unordered_set>
 #include <vector>
 
@@ -39,15 +40,10 @@
 #include "g2o/stuff/string_tools.h"
 
 namespace {
-std::ostream& operator<<(std::ostream& os, const std::vector<double>& v) {
-  for (size_t i = 0; i < v.size(); ++i) {
-    if (i > 0) os << " ";
-    os << v[i];
-  }
-  return os;
-}
-
-std::ostream& operator<<(std::ostream& os, const std::vector<int>& v) {
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const std::vector<T>& v) {
+  static_assert(std::is_integral_v<T> || std::is_floating_point_v<T>,
+                "Type has to be integral or floating point");
   for (size_t i = 0; i < v.size(); ++i) {
     if (i > 0) os << " ";
     os << v[i];