feat: add boolean operator (#98)

* feat: add `Error::operator bool()` operator

* fix: mark `Error::operator bool` as explicit

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;