diff --git a/src/const/private/const.cpp b/src/const/private/const.cpp
index efa8f4b..c1e21b0 100644
--- a/src/const/private/const.cpp
+++ b/src/const/private/const.cpp
@@ -19,11 +19,7 @@ bool constants::initialize(const std::string& filename) {
   return load(filename);
 }
 
-constant constants::get(const std::string& name) {
-  return constants_[name];
-}
-
-constant constants::operator[](const std::string& name) const {
+constant constants::get(const std::string& name) const {
   auto it = constants_.find(name);
   if (it != constants_.end()) {
     return it->second;
@@ -32,6 +28,10 @@ constant constants::operator[](const std::string& name) const {
   }
 }
 
+constant constants::operator[](const std::string& name) const {
+  return this->get(name);
+}
+
 bool constants::has(const std::string& name) const {
   return constants_.find(name) != constants_.end();
 }
@@ -50,9 +50,9 @@ std::string constants::trim(const std::string& str) {
     size_t last = str.find_last_not_of(" \t");
     return str.substr(first, last - first + 1);
 }
+
 bool constants::load(const std::string& filename) {
     std::ifstream file(filename);
-    std::map<std::string, constant> constants_temp;
     if (!file.is_open()) {
         std::cerr << "Error: Unable to open file " << filename << std::endl;
         return false;
@@ -81,12 +81,12 @@ bool constants::load(const std::string& filename) {
         // Define exact column widths from Python script
         int start = 0;
 
-        std::string symbol       = trim(line.substr(start, col_widths_[0])); start += col_widths_[0];
-        std::string name         = trim(line.substr(start, col_widths_[1])); start += col_widths_[1];
-        std::string valueStr     = line.substr(start, col_widths_[2]); start += col_widths_[2];
-        std::string unit         = trim(line.substr(start, col_widths_[3])); start += col_widths_[3]; // Only trim the unit
-        std::string uncertaintyStr = line.substr(start, col_widths_[4]); start += col_widths_[4];
-        std::string reference    = trim(line.substr(start, col_widths_[5])); // Only trim reference
+        const std::string symbol       = trim(line.substr(start, col_widths_[0])); start += col_widths_[0];
+        const std::string name         = trim(line.substr(start, col_widths_[1])); start += col_widths_[1];
+        const std::string valueStr     = line.substr(start, col_widths_[2]); start += col_widths_[2];
+        const std::string unit         = trim(line.substr(start, col_widths_[3])); start += col_widths_[3]; // Only trim the unit
+        const std::string uncertaintyStr = line.substr(start, col_widths_[4]); start += col_widths_[4];
+        const std::string reference    = trim(line.substr(start, col_widths_[5])); // Only trim reference
 
         // Convert numerical fields safely
         double value = 0.0, uncertainty = 0.0;
@@ -102,11 +102,10 @@ bool constants::load(const std::string& filename) {
         }
 
         // Store in map
-        constants_temp[symbol] = {name, value, uncertainty, unit, reference};
+        constants_.emplace(symbol, constant{name, value, uncertainty, unit, reference});
     }
 
     file.close();
-    constants_ = constants_temp;
     loaded_ = true;
     return true;
 }
diff --git a/src/const/public/const.h b/src/const/public/const.h
index eae184c..146a221 100644
--- a/src/const/public/const.h
+++ b/src/const/public/const.h
@@ -11,11 +11,22 @@
  * @brief Structure to hold a constant's details.
  */
 struct constant {
-  std::string name;         ///< Name of the constant
-  double value;             ///< Value of the constant
-  double uncertainty;       ///< Uncertainty in the constant's value
-  std::string unit;         ///< Unit of the constant
-  std::string reference;    ///< Reference for the constant's value
+  const std::string name;         ///< Name of the constant
+  const double value;             ///< Value of the constant
+  const double uncertainty;       ///< Uncertainty in the constant's value
+  const std::string unit;         ///< Unit of the constant
+  const std::string reference;    ///< Reference for the constant's value
+
+  /**
+   * @brief Parameterized constructor.
+   * @param name The name of the constant.
+   * @param value The value of the constant.
+   * @param uncertainty The uncertainty in the constant's value.
+   * @param unit The unit of the constant.
+   * @param reference The reference for the constant's value.
+   */
+  constant(const std::string& name, double value, double uncertainty, const std::string& unit, const std::string& reference)
+    : name(name), value(value), uncertainty(uncertainty), unit(unit), reference(reference) {}
 
   /**
    * @brief overload the << operator for pretty printing
@@ -81,7 +92,7 @@ public:
    * @param key The name of the constant to retrieve.
    * @return The constant associated with the given key.
    */
-  constant get(const std::string& key);
+  constant get(const std::string& key) const;
 
   /**
    * @brief Overloaded subscript operator to access constants by key.