2-nd phase: add 'stout::expected' alias and some tests for it

Author: ArthurBandaryk

include/stout/expected.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "tl/expected.hpp"
+
+////////////////////////////////////////////////////////////////////////
+
+namespace stout {
+
+////////////////////////////////////////////////////////////////////////
+
+// Define aliases for 'tl::expected', 'tl::unexpected' and
+// 'tl::make_unexpected' that are used to represent error-or-value types
+// returned by code throughout stout. Errors are std::strings, and the
+// error-or-value type is similar to C++23's std::expected.
+// You can read more about 'tl::expected' library using the link below:
+// https://github.com/TartanLlama/expected
+
+template <typename T, typename Error = std::string>
+using expected = tl::expected<T, Error>;
+
+template <typename Error = std::string>
+using unexpected = tl::unexpected<Error>;
+
+template <typename Error>
+auto make_unexpected = tl::make_unexpected<Error>;
+
+////////////////////////////////////////////////////////////////////////
+
+} // namespace stout
+
+////////////////////////////////////////////////////////////////////////

tests/BUILD.bazel

@@ -39,6 +39,7 @@ cc_test(
 cc_test(
     name = "stout",
     srcs = [
+        "expected_tests.cc",
         "stringify_tests.cc",
         "temporary_directory_test_tests.cc",
     ],

tests/expected_tests.cc

@@ -0,0 +1,37 @@
+#include "gtest/gtest.h"
+#include "stout/expected.h"
+
+stout::expected<int> divide(const int dividend, const int divisor) {
+  if (divisor == 0) {
+    return stout::make_unexpected<std::string>("divide by zero");
+  }
+
+  return dividend / divisor;
+}
+
+TEST(Expected, SucceedResult) {
+  const stout::expected<int> result = divide(6, 3);
+
+  EXPECT_EQ(result, stout::expected<int>(2));
+}
+
+TEST(Expected, DivideByZero) {
+  const stout::expected<int> result = divide(6, 0);
+
+  EXPECT_EQ(result, stout::make_unexpected<std::string>("divide by zero"));
+}
+
+TEST(Expected, MakeUnexpected) {
+  auto error = []() {
+    return stout::make_unexpected<std::string>("error");
+  };
+  const stout::unexpected<std::string> result = error();
+
+  EXPECT_EQ("error", result.value());
+}
+
+TEST(Expected, Unexpected) {
+  stout::unexpected<std::string> unexpected{"error"};
+
+  EXPECT_EQ("error", unexpected.value());
+}