Store Message as a Shared Constant String

docs/index.rst

@@ -12,7 +12,7 @@ API Docs
 
 .. doxygenfunction:: errors::format
 
-.. doxygenstruct:: errors::Error
+.. doxygenclass:: errors::Error
    :members:
 
 License

include/errors/error.hpp

@@ -2,6 +2,7 @@
 
 #include <fmt/core.h>
 
+#include <memory>
 #include <ostream>
 #include <string>
 #include <utility>
@@ -11,8 +12,24 @@ namespace errors {
 /**
  * @brief Represents error information.
  */
-struct Error {
-  const std::string message; /**< The error message. */
+class Error {
+ private:
+  const std::shared_ptr<const std::string> message_ptr;
+
+ public:
+  Error(const std::shared_ptr<const std::string>& message_ptr);
+
+  /**
+   * @brief Returns the error message.
+   *
+   * @code{.cpp}
+   * const auto err = errors::make("unknown error");
+   *
+   * // Print "unknown error"
+   * std::cout << err << std::endl;
+   * @endcode
+   */
+  std::string message() const;
 
   /**
    * @brief Writes the string representation of an error object to the given

src/error.cpp

@@ -2,19 +2,28 @@
 
 namespace errors {
 
+Error::Error(const std::shared_ptr<const std::string>& message_ptr) : message_ptr(message_ptr) {}
+
+std::string Error::message() const {
+  if (!message_ptr) return "no error";
+  return *message_ptr;
+}
+
 std::ostream& operator<<(std::ostream& os, const errors::Error& err) {
-  return os << "error: " << err.message;
+  return os << "error: " << err.message();
 }
 
 bool operator==(const Error& lhs, const Error& rhs) {
-  return lhs.message == rhs.message;
+  return lhs.message() == rhs.message();
 }
 
 bool operator!=(const Error& lhs, const Error& rhs) {
-  return lhs.message != rhs.message;
+  return lhs.message() != rhs.message();
 }
 
-Error make(const std::string& msg) { return Error{.message = msg}; }
+Error make(const std::string& msg) {
+  return Error(std::make_shared<const std::string>(msg));
+}
 
 }  // namespace error
 
@@ -27,7 +36,7 @@ format_parse_context::iterator formatter<errors::Error>::parse(
 
 format_context::iterator formatter<errors::Error>::format(
     const errors::Error& err, format_context& ctx) const {
-  return format_to(ctx.out(), "error: {}", err.message);
+  return format_to(ctx.out(), "error: {}", err.message());
 }
 
 }  // namespace fmt

test/error_test.cpp

@@ -7,12 +7,12 @@
 
 TEST_CASE("Error Construction") {
   const errors::Error err = errors::make("unknown error");
-  REQUIRE(err.message == "unknown error");
+  REQUIRE(err.message() == "unknown error");
 }
 
 TEST_CASE("Error Construction With Formatting") {
   const errors::Error err = errors::format("HTTP error {}", 404);
-  REQUIRE(err.message == "HTTP error 404");
+  REQUIRE(err.message() == "HTTP error 404");
 }
 
 TEST_CASE("Error Comparison") {