Add Boolean Operator

include/errors/error.hpp

@@ -30,6 +30,23 @@ class Error {
    */
   std::string_view message() const;
 
+  /**
+   * @brief Checks whether the object contains an error.
+   * @return `true` if it contains an error, otherwise `false`.
+   *
+   * @code{.cpp}
+   * const auto err = errors::make("unknown error");
+   *
+   * // Print "contains error".
+   * if (err) {
+   *   std::cout << "contains error" << std::endl;
+   * } else {
+   *   std::cout << "no error" << std::endl;
+   * }
+   * @endcode
+   */
+  explicit operator bool() const;
+
   friend Error make(const std::string& msg);
 
   /**

src/error.cpp

@@ -9,6 +9,10 @@ std::string_view Error::message() const {
   return *message_ptr;
 }
 
+Error::operator bool() const {
+  return (bool)message_ptr;
+}
+
 std::ostream& operator<<(std::ostream& os, const errors::Error& err) {
   return os << "error: " << err.message();
 }

test/error_test.cpp

@@ -7,6 +7,11 @@ TEST_CASE("Error Construction") {
   REQUIRE(err.message() == "unknown error");
 }
 
+TEST_CASE("Error Checking") {
+  const auto err = errors::make("unknown error");
+  REQUIRE(err);
+}
+
 TEST_CASE("Error Printing Using OStream") {
   const auto err = errors::make("unknown error");
   const auto ss = std::stringstream() << err;