From 834d5d5964a59a839c8844fa60a79ca798d8adf6 Mon Sep 17 00:00:00 2001
From: David Chen <36295559+David0922@users.noreply.github.com>
Date: Sun, 21 Dec 2025 05:07:04 +0800
Subject: [PATCH] C++ 23 -> C++ 20; std::expected -> Expected (#3)

---
 CMakeLists.txt | 11 +++++++----
 src/main.cc    | 18 +++++++++---------
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 287ebda..b064c43 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,16 +1,19 @@
 cmake_minimum_required(VERSION 3.16)
 
+project(redis_playground LANGUAGES CXX)
+
 set(CMAKE_CXX_EXTENSIONS OFF)
-set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2")
 
-project(redis_playground LANGUAGES CXX)
-
 find_package(hiredis CONFIG REQUIRED)
 
 add_library(proj_warnings INTERFACE)
 target_compile_options(proj_warnings INTERFACE -Wall -Werror -Wextra -Wpedantic)
 
+add_library(expected INTERFACE src/expected.h)
+target_link_libraries(expected INTERFACE proj_warnings)
+
 add_executable(main ./src/main.cc)
-target_link_libraries(main PRIVATE proj_warnings hiredis::hiredis)
+target_link_libraries(main PRIVATE proj_warnings expected hiredis::hiredis)
diff --git a/src/main.cc b/src/main.cc
index 4b24486..8a84956 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -1,6 +1,5 @@
 #include <hiredis/hiredis.h>
 
-#include <expected>
 #include <format>
 #include <iostream>
 #include <memory>
@@ -12,6 +11,8 @@
 #include <unordered_map>
 #include <vector>
 
+#include "expected.h"
+
 struct FieldVal {
   std::string field, val;
 };
@@ -73,7 +74,7 @@ class RedisClient {
     if (ctx_) redisFree(ctx_);
   }
 
-  std::expected<void, std::string> xadd(const XaddReq& req) noexcept {
+  Expected<void> xadd(const XaddReq& req) noexcept {
     // todo: safe guard against invalid requests
 
     std::stringstream ss;
@@ -84,15 +85,15 @@ class RedisClient {
     auto reply = submit_cmd(ss.str());
 
     if (!reply) {
-      return std::unexpected(ctx_->errstr);
+      return Unexpected(ctx_->errstr);
     } else if (reply->type == REDIS_REPLY_ERROR) {
-      return std::unexpected(reply->str ? reply->str : "unknown error");
+      return Unexpected(reply->str ? reply->str : "unknown error");
     }
 
     return {};
   }
 
-  std::expected<XreadRes, std::string> xread(const XreadReq& req) noexcept {
+  Expected<XreadRes> xread(const XreadReq& req) noexcept {
     // todo: safe guard against invalid requests
 
     std::stringstream ss;
@@ -105,14 +106,13 @@ class RedisClient {
     auto reply = submit_cmd(ss.str());
 
     if (!reply) {
-      return std::unexpected(ctx_->errstr);
+      return Unexpected(ctx_->errstr);
     } else if (reply->type == REDIS_REPLY_ERROR) {
-      return std::unexpected(reply->str ? reply->str : "unknown reply error");
+      return Unexpected(reply->str ? reply->str : "unknown reply error");
     } else if (reply->type == REDIS_REPLY_NIL) {
       return {};
     } else if (reply->type != REDIS_REPLY_ARRAY) {
-      return std::unexpected(
-          std::format("unexpected reply type {}", reply->type));
+      return Unexpected(std::format("unexpected reply type {}", reply->type));
     }
 
     XreadRes res;