diff --git a/.gitignore b/.gitignore
index 7477ecc4..f289fea6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -111,3 +111,5 @@ fabric.properties
 
 # Android studio 3.1+ serialized cache file
 .idea/caches/build_file_checksums.ser
+
+webserv
\ No newline at end of file
diff --git a/Makefile b/Makefile
index ec6c3e12..b1988b6f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,28 @@
-all:
+NAME := webserv
+SRC_DIR := src
+SRCS := $(shell find $(SRC_DIR) -name '*.cpp')
+BUILD_DIR := dist
+OBJS := $(addprefix $(BUILD_DIR)/,$(SRCS:.cpp=.o))
+CXXFLAGS := -std=c++98 -I$(SRC_DIR)/lib -Wall -Wextra -Werror
+
+all: $(NAME)
+
+$(NAME): $(OBJS)
+	$(CXX) $(CXXFLAGS) -o $(NAME) $(OBJS)
+
+$(BUILD_DIR)/%.o: %.cpp
+	@mkdir -p $(dir $@)
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+clean:
+	rm -rf $(BUILD_DIR)
+
+fclean: clean
+	rm -rf $(NAME)
+
+re: fclean all
 
 format:
-	clang-format -i $$(git ls-files '*.cpp' '*.hpp')
\ No newline at end of file
+	clang-format -i $$(git ls-files '*.cpp' '*.hpp')
+
+.PHONY: all clean fclean re format
\ No newline at end of file
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ea8788b7..4913b605 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,4 +1,4 @@
-set(CMAKE_CXX_STANDARD 11)  # TODO: C++98 にする
+set(CMAKE_CXX_STANDARD 98)  # TODO: C++98 にする
 # 実行ファイルを /bin に出力
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_SOURCE_DIR}/bin)
 
diff --git a/src/cmd/main.cpp b/src/cmd/main.cpp
index 3e2c5fbb..0a5d8bb9 100644
--- a/src/cmd/main.cpp
+++ b/src/cmd/main.cpp
@@ -10,6 +10,8 @@ int main(const int argc, char *argv[]) {
         return 1;
     }
 
+    SET_LOG_LEVEL(Logger::kInfo);
+
     const Option<Config> config = Config::loadConfigFromFile(argv[1]);
     if (config.isNone()) {
         return 1;
diff --git a/src/lib/cgi/factory.cpp b/src/lib/cgi/factory.cpp
index 885dec5a..ab3a90f5 100644
--- a/src/lib/cgi/factory.cpp
+++ b/src/lib/cgi/factory.cpp
@@ -68,7 +68,7 @@ namespace cgi {
         http::Headers headers(res.getHeaders());
 
         // 200 がデフォルト、Status ヘッダーがあればそれを使う
-        const http::Headers::const_iterator statusHeader = headers.find("Status");
+        const http::Headers::iterator statusHeader = headers.find("Status");
         http::HttpStatusCode status = http::kStatusOk;
         if (statusHeader != headers.end()) {
             status = TRY(HttpResponseFactory::statusFromHeader(statusHeader->second)).unwrapOr(http::kStatusOk);
diff --git a/src/lib/config/config.cpp b/src/lib/config/config.cpp
index dc8a1aa4..9f665619 100644
--- a/src/lib/config/config.cpp
+++ b/src/lib/config/config.cpp
@@ -1,12 +1,10 @@
 #include "config.hpp"
-
 #include "http/handler/middleware/logger.hpp"
 #include "toml/parser.hpp"
 #include "toml/value.hpp"
 #include "utils/logger.hpp"
-
+#include <cstdlib>
 #include <fstream>
-#include <iostream>
 
 namespace config {
     /* Config */
@@ -27,7 +25,7 @@ namespace config {
 
     Option<Config> Config::loadConfigFromFile(const std::string &path) {
         try {
-            std::ifstream configFile(path);
+            std::ifstream configFile(path.c_str());
             if (!configFile.is_open()) {
                 LOG_ERRORF("cannot open config file: %s", path.c_str());
                 return None;
@@ -117,7 +115,7 @@ namespace config {
             toml::Table errorPageTable = serverTable.getValue("error_page").unwrap().getTable().unwrap();
             std::vector<std::string> keys = errorPageTable.getKeys();
             for (size_t j = 0; j < keys.size(); ++j) {
-                int statusCode = std::stoi(keys[j]);
+                int statusCode = static_cast<int>(std::strtol(keys[j].c_str(), NULL, 10));
                 Option<http::HttpStatusCode> httpStatusCode = http::httpStatusCodeFromInt(statusCode);
                 if (httpStatusCode.isNone()) {
                     LOG_WARNF("invalid HTTP status code: %d", statusCode);
@@ -242,7 +240,7 @@ namespace config {
             for (size_t k = 0; k < methodValues.size(); ++k) {
                 std::string methodStr = methodValues[k].getString().unwrap();
                 http::HttpMethod method = http::httpMethodFromString(methodStr);
-                if (method == http::HttpMethod::kMethodUnknown) {
+                if (method == http::kMethodUnknown) {
                     LOG_ERRORF("unknown http method: %s", methodStr.c_str());
                     throw std::runtime_error("unknown method: " + methodStr);
                 }
diff --git a/src/lib/config/toml/parser.cpp b/src/lib/config/toml/parser.cpp
index 60a3fc77..7ca891f6 100644
--- a/src/lib/config/toml/parser.cpp
+++ b/src/lib/config/toml/parser.cpp
@@ -1,6 +1,11 @@
 #include "parser.hpp"
+
+#include "utils/fd.hpp"
+#include "utils/string.hpp"
 #include "utils/types/try.hpp"
 
+#include <cstdlib>
+
 namespace toml {
     TomlParser::TomlParser(const Tokenizer::Tokens &tokens)
         : tokens_(tokens), pos_(0), nextPos_(0), token_(kUnknown, "") {
@@ -34,7 +39,7 @@ namespace toml {
             return Ok(t);
         }
 
-        return Err(error::AppError::kParseUnknown);
+        return Err(error::kParseUnknown);
     }
 
     void TomlParser::consumeNewlines() {
@@ -80,7 +85,7 @@ namespace toml {
         TRY(expect(kRBracket));
 
         if (keys.empty()) {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         Table *currentTable = TRY(table.findOrCreateTablePath(keys));
@@ -93,12 +98,12 @@ namespace toml {
             if (value.getType() == Value::kArray) {
                 Array &array = value.getArrayRef();
                 if (array.size() == 0) {
-                    return Err(error::AppError::kParseUnknown);
+                    return Err(error::kParseUnknown);
                 }
                 array.addElement(Value(newTable));
                 currentTable = &array.getElementRef(array.size() - 1).getTableRef();
             } else {
-                return Err(error::AppError::kParseUnknown);
+                return Err(error::kParseUnknown);
             }
         } else {
             Array array;
@@ -116,7 +121,7 @@ namespace toml {
         TRY(expect(kRBracket));
 
         if (keys.empty()) {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         Table *currentTable = TRY(table.findOrCreateTablePath(keys));
@@ -124,7 +129,7 @@ namespace toml {
         const Table newTable;
 
         if (currentTable->getValue(lastKey).isSome()) {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         currentTable->setValue(lastKey, Value(newTable));
@@ -140,7 +145,7 @@ namespace toml {
         Value val = TRY(parseVal());
 
         if (keys.empty()) {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         if (keys.size() == 1) {
@@ -200,7 +205,7 @@ namespace toml {
             value = Value(token_.getValue());
             nextToken();
         } else if (peek(kNum)) {
-            value = Value(std::stol(token_.getValue()));
+            value = Value(std::strtol(token_.getValue().c_str(), NULL, 10));
             nextToken();
         } else if (peek(kLBracket)) {
             nextToken();
@@ -246,7 +251,7 @@ namespace toml {
             table = table.readOnly();
             value = Value(table);
         } else {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         return Ok(value);
diff --git a/src/lib/config/toml/value.cpp b/src/lib/config/toml/value.cpp
index 3a8e2d4d..b302337f 100644
--- a/src/lib/config/toml/value.cpp
+++ b/src/lib/config/toml/value.cpp
@@ -246,7 +246,7 @@ namespace toml {
 
     Result<Table *, error::AppError> Table::findOrCreateTablePath(const std::vector<std::string> &keys) {
         if (keys.empty()) {
-            return Err(error::AppError::kParseUnknown);
+            return Err(error::kParseUnknown);
         }
 
         const size_t endIndex = keys.size() - 1;
@@ -271,11 +271,11 @@ namespace toml {
                         if (lastElement.getType() == Value::kTable) {
                             currentTable = &lastElement.getTableRef();
                         } else {
-                            return Err(error::AppError::kParseUnknown);
+                            return Err(error::kParseUnknown);
                         }
                     }
                 } else {
-                    return Err(error::AppError::kParseUnknown);
+                    return Err(error::kParseUnknown);
                 }
             } else {
                 Table newTable;
diff --git a/src/lib/core/action/run_cgi_action.cpp b/src/lib/core/action/run_cgi_action.cpp
index 8c8dbc2a..d561ac0a 100644
--- a/src/lib/core/action/run_cgi_action.cpp
+++ b/src/lib/core/action/run_cgi_action.cpp
@@ -10,6 +10,7 @@
 #include "utils/fd.hpp"
 #include "utils/time.hpp"
 #include "utils/logger.hpp"
+#include <cstdlib>
 
 void RunCgiAction::execute(ActionContext &ctx) {
     int pair[2];
@@ -135,6 +136,7 @@ void RunCgiAction::parentRoutine(const ActionContext &ctx, const int socketFd, c
     ctx.getState().getEventNotifier().unregisterEvent(Event(clientFd_, Event::kWrite));
     ctx.getState().getEventHandlerRepository().remove(clientFd_, Event::kRead);
     ctx.getState().getEventHandlerRepository().remove(clientFd_, Event::kWrite);
-    CgiProcessRepository::Data data = {clientFd_, socketFd, utils::Time::getCurrentTime()};
+
+    const CgiProcessRepository::Data data = {clientFd_, socketFd, utils::Time::getCurrentTime()};
     ctx.getState().getCgiProcessRepository().set(childPid, data);
 }
diff --git a/src/lib/core/action/serve_http_action.cpp b/src/lib/core/action/serve_http_action.cpp
index 9a5b328a..f29960c6 100644
--- a/src/lib/core/action/serve_http_action.cpp
+++ b/src/lib/core/action/serve_http_action.cpp
@@ -9,7 +9,7 @@ void ServeHttpAction::execute(ActionContext &actionCtx) {
     const Option<Ref<VirtualServer> > vs = eventCtx_.getResolver().unwrap().resolve(hostHeader);
 
     // accept したので Connection, VirtualServer は存在するはず
-    const http::RequestContext reqContext(req_, eventCtx_.getConnection().unwrap());
+    const http::RequestContext reqContext(req_, eventCtx_.getConnection().unwrap().toConst());
     const Either<IAction *, http::Response> resOrAction = vs.unwrap().get().getRouter().serve(reqContext);
     if (resOrAction.isLeft()) {
         LOG_DEBUG("ServeHttpAction: action is returned");
diff --git a/src/lib/core/child_reaper.cpp b/src/lib/core/child_reaper.cpp
index 57fe71cc..322e3455 100644
--- a/src/lib/core/child_reaper.cpp
+++ b/src/lib/core/child_reaper.cpp
@@ -1,5 +1,6 @@
 #include "child_reaper.hpp"
 #include <sys/wait.h>
+#include <cerrno>
 
 void ChildReaper::attachToEventNotifier(IEventNotifier *notifier) const {
     selfPipe_.registerWithEventNotifier(notifier);
@@ -12,7 +13,8 @@ std::vector<ChildReaper::ReapedProcess> ChildReaper::onSignalEvent() const {
     while (true) {
         int status = 0;
         const pid_t pid = waitpid(-1, &status, WNOHANG);
-        result.push_back({pid, WEXITSTATUS(status)});
+        const ReapedProcess rp = {pid, WEXITSTATUS(status)};
+        result.push_back(rp);
 
         if (pid > 0) {
             continue;
diff --git a/src/lib/core/handler/read_cgi_response_handler.cpp b/src/lib/core/handler/read_cgi_response_handler.cpp
index c3189bf7..fe0c9b32 100644
--- a/src/lib/core/handler/read_cgi_response_handler.cpp
+++ b/src/lib/core/handler/read_cgi_response_handler.cpp
@@ -20,7 +20,7 @@ IEventHandler::InvokeResult ReadCgiResponseHandler::invoke(const Context &ctx) {
     const ssize_t bytesRead = read(conn.getFd(), buffer, sizeof(buffer));
     if (bytesRead == -1) {
         LOG_WARN("failed to read CGI response");
-        return Err(error::AppError::kUnknown);
+        return Err(error::kUnknown);
     }
 
     if (bytesRead != 0) {
@@ -36,7 +36,8 @@ IEventHandler::InvokeResult ReadCgiResponseHandler::invoke(const Context &ctx) {
 }
 
 IEventHandler::ErrorHandleResult ReadCgiResponseHandler::onErrorEvent(const Context &, const Event &event) {
-    LOG_WARNF("ReadCgiResponseHandler received an error event %d", event.getTypeFlags());
+    // 結構うるさいので debug にする
+    LOG_DEBUGF("ReadCgiResponseHandler received an error event %d", event.getTypeFlags());
 
     if (event.getTypeFlags() & Event::kHangUp) {
         return ErrorHandleResult(false, std::vector<IAction *>());
@@ -115,8 +116,8 @@ Result<cgi::Response, error::AppError> ReadCgiResponseHandler::createCgiResponse
     std::istringstream headerStream(headerPart);
     std::string line;
     while (std::getline(headerStream, line)) {
-        if (!line.empty() && line.back() == '\r') {
-            line.pop_back();
+        if (!line.empty() && line[line.length() - 1] == '\r') {
+            line = line.substr(0, line.length() - 1);
         }
         const http::RequestParser::ParseHeaderFieldLineResult result = http::RequestParser::parseHeaderFieldLine(line);
         if (result.isOk()) {
diff --git a/src/lib/core/handler/read_request_handler.cpp b/src/lib/core/handler/read_request_handler.cpp
index c635870d..288c44c6 100644
--- a/src/lib/core/handler/read_request_handler.cpp
+++ b/src/lib/core/handler/read_request_handler.cpp
@@ -15,7 +15,7 @@ ReadRequestHandler::ReadRequestHandler(const VirtualServerResolver &vsResolver)
 
 IEventHandler::InvokeResult ReadRequestHandler::invoke(const Context &ctx) {
     LOG_DEBUG("start ReadRequestHandler");
-    const auto conn = ctx.getConnection().unwrap();
+    const Ref<Connection> conn = ctx.getConnection().unwrap();
 
     // アクティビティを更新
     ctx.getConnection().unwrap().get().updateActivity();
diff --git a/src/lib/core/handler/write_cgi_request_handler.cpp b/src/lib/core/handler/write_cgi_request_handler.cpp
index 9c55b8a0..627b136a 100644
--- a/src/lib/core/handler/write_cgi_request_handler.cpp
+++ b/src/lib/core/handler/write_cgi_request_handler.cpp
@@ -1,3 +1,4 @@
+#include <cerrno>
 #include <unistd.h>
 #include <sys/socket.h>
 #include "write_cgi_request_handler.hpp"
diff --git a/src/lib/core/server.cpp b/src/lib/core/server.cpp
index 594d0eaa..314be65e 100644
--- a/src/lib/core/server.cpp
+++ b/src/lib/core/server.cpp
@@ -10,6 +10,7 @@
 #include <map>
 #include <signal.h>
 #include <cstring>
+#include <cerrno>
 
 Server::Server(const config::Config &config) : config_(config) {
     const config::ServerContextList &servers = config_.getServers();
@@ -125,7 +126,9 @@ void Server::start() {
 void Server::invokeHandlers(const Context &ctx) {
     const Event &event = ctx.getEvent();
 
-    const std::vector<Event::EventType> types = {Event::kRead, Event::kWrite};
+    std::vector<Event::EventType> types;
+    types.push_back(Event::kRead);
+    types.push_back(Event::kWrite);
     // TODO: handler の呼び方が壊れてる
     for (std::vector<Event::EventType>::const_iterator it = types.begin(); it != types.end(); ++it) {
         const Event::EventType type = *it;
diff --git a/src/lib/core/virtual_server_resolver.cpp b/src/lib/core/virtual_server_resolver.cpp
index 50007569..9fae2a42 100644
--- a/src/lib/core/virtual_server_resolver.cpp
+++ b/src/lib/core/virtual_server_resolver.cpp
@@ -51,5 +51,5 @@ VirtualServerResolverFactory::VirtualServerResolverFactory(const VirtualServerLi
     : virtualServers_(virtualServers) {}
 
 VirtualServerResolver VirtualServerResolverFactory::create(const Ref<Connection> &conn) {
-    return VirtualServerResolver(virtualServers_, conn);
+    return VirtualServerResolver(virtualServers_, conn.toConst());
 }
diff --git a/src/lib/event/event_notifier.cpp b/src/lib/event/event_notifier.cpp
index 5049f301..ca37ca0d 100644
--- a/src/lib/event/event_notifier.cpp
+++ b/src/lib/event/event_notifier.cpp
@@ -171,7 +171,8 @@ IEventNotifier::WaitEventsResult PollEventNotifier::waitEvents(int timeoutMs) {
 
     const int result = poll(fds.data(), fds.size(), timeoutMs);
     if (result == -1) {
-        LOG_ERRORF("poll failed: %s", std::strerror(errno));
+        // EINTR が起こりがちなので、debug にしておく
+        LOG_DEBUGF("poll failed: %s", std::strerror(errno));
         return Err(error::kUnknown);
     }
 
diff --git a/src/lib/http/handler/cgi_handler.cpp b/src/lib/http/handler/cgi_handler.cpp
index 9d19e37a..4df9608a 100644
--- a/src/lib/http/handler/cgi_handler.cpp
+++ b/src/lib/http/handler/cgi_handler.cpp
@@ -10,7 +10,7 @@
 // めんどくさくてメソッドにしてない
 static bool fileExistsUnderRoot(const std::string &docRoot, const std::string &urlPath) {
     std::string fsPath = docRoot;
-    if (!fsPath.empty() && fsPath.back() != '/') fsPath += '/';
+    if (!fsPath.empty() && fsPath[fsPath.length() - 1] != '/') fsPath += '/';
     if (!urlPath.empty() && urlPath[0] == '/')
         fsPath += urlPath.substr(1);
     else
diff --git a/src/lib/http/handler/delete_file_handler.cpp b/src/lib/http/handler/delete_file_handler.cpp
index 31786785..f102e6a4 100644
--- a/src/lib/http/handler/delete_file_handler.cpp
+++ b/src/lib/http/handler/delete_file_handler.cpp
@@ -2,6 +2,8 @@
 #include "http/response/response_builder.hpp"
 #include "utils/logger.hpp"
 #include <sys/stat.h>
+#include <cerrno>
+#include <cstdio>
 
 namespace http {
     DeleteFileHandler::DeleteFileHandler(const config::LocationContext::DocumentRootConfig &docRootConfig)
diff --git a/src/lib/http/handler/middleware/error_page.cpp b/src/lib/http/handler/middleware/error_page.cpp
index d550f6eb..26cb782b 100644
--- a/src/lib/http/handler/middleware/error_page.cpp
+++ b/src/lib/http/handler/middleware/error_page.cpp
@@ -23,7 +23,7 @@ Either<IAction *, http::Response> http::ErrorPage::intercept(const RequestContex
     config::ServerContext::ErrorPageMap::iterator customErrorPage = errorPage_.find(status);
 
     if (customErrorPage != errorPage_.end()) {
-        std::ifstream file(customErrorPage->second);
+        std::ifstream file(customErrorPage->second.c_str());
         std::stringstream buf;
         buf << file.rdbuf();
         body = buf.str();
diff --git a/src/lib/http/handler/upload_file_handler.cpp b/src/lib/http/handler/upload_file_handler.cpp
index 3c3a586f..a283d3b3 100644
--- a/src/lib/http/handler/upload_file_handler.cpp
+++ b/src/lib/http/handler/upload_file_handler.cpp
@@ -230,7 +230,8 @@ http::UploadFileHandler::processMultipartPart(const std::string &headers, std::s
     // ヘッダーをCRLFで分割
     const std::vector<std::string> headerLines = splitHeadersByNewline(headers);
 
-    for (const std::string &headerLine : headerLines) {
+    for (size_t i = 0; i < headerLines.size(); i++) {
+        const std::string &headerLine = headerLines[i];
         // 空行や不正な形式の行はスキップ
         if (headerLine.empty()) {
             continue;
@@ -286,7 +287,8 @@ void http::UploadFileHandler::processContentDispositionHeader(
     // 各パラメータをセミコロンで分割
     const std::vector<std::string> params = utils::split(headerValue, ';');
 
-    for (const std::string &param : params) {
+    for (size_t i = 0; i < params.size(); i++) {
+        const std::string &param = params[i];
         std::string trimmedParam = utils::trim(param);
 
         // name属性の処理
@@ -317,7 +319,7 @@ http::Response
 http::UploadFileHandler::saveUploadedFile(const std::string &filename, const std::string &content) const {
     const std::string filePath = docConfig_.getRoot() + "/" + filename;
 
-    std::ofstream outFile(filePath, std::ios::binary);
+    std::ofstream outFile(filePath.c_str(), std::ios::binary);
     if (!outFile) {
         return ResponseBuilder().status(kStatusConflict).text("Failed to open file for writing: " + filename).build();
     }
diff --git a/src/lib/http/request/reader/reading_body_state.cpp b/src/lib/http/request/reader/reading_body_state.cpp
index f828c627..79f619fe 100644
--- a/src/lib/http/request/reader/reading_body_state.cpp
+++ b/src/lib/http/request/reader/reading_body_state.cpp
@@ -11,7 +11,7 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError> http::Reading
         const std::size_t want = contentLength_ - body_.size();
         const std::string chunk = readBuf.consume(want);
         if (chunk.empty()) {
-            return Ok(HandleStatus::kSuspend);
+            return Ok(kSuspend);
         }
         body_ += chunk;
     }
@@ -19,5 +19,5 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError> http::Reading
     ctx_.setBody(body_);
     ctx_.changeState(NULL);
 
-    return Ok(HandleStatus::kDone);
+    return Ok(kHandleDone);
 }
diff --git a/src/lib/http/request/reader/reading_chunked_body_state.cpp b/src/lib/http/request/reader/reading_chunked_body_state.cpp
index abebfc3f..c48d7e82 100644
--- a/src/lib/http/request/reader/reading_chunked_body_state.cpp
+++ b/src/lib/http/request/reader/reading_chunked_body_state.cpp
@@ -30,7 +30,7 @@ namespace http {
         while (state_ != kDone) {
             const Option<std::string> maybeLine = TRY(getLine(readBuf));
             if (maybeLine.isNone()) {
-                return Ok(HandleStatus::kSuspend);
+                return Ok(kSuspend);
             }
             const std::string &line = maybeLine.unwrap();
 
@@ -78,7 +78,7 @@ namespace http {
         ctx_.setBody(body_);
         ctx_.changeState(NULL);
 
-        return Ok(HandleStatus::kDone);
+        return Ok(kHandleDone);
     }
 
     Result<std::size_t, error::AppError> ReadingChunkedBodyState::parseChunkSizeLine(const std::string &line) {
diff --git a/src/lib/http/request/reader/reading_headers_state.cpp b/src/lib/http/request/reader/reading_headers_state.cpp
index 53c3c591..546c7aba 100644
--- a/src/lib/http/request/reader/reading_headers_state.cpp
+++ b/src/lib/http/request/reader/reading_headers_state.cpp
@@ -14,7 +14,7 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError> http::Reading
         const Option<std::string> line = TRY(getLine(readBuf));
         if (line.isNone()) {
             // バッファが足りない
-            return Ok(HandleStatus::kSuspend);
+            return Ok(kSuspend);
         }
 
         /**
@@ -31,7 +31,7 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError> http::Reading
     ctx_.setHeaders(headers_);
     ctx_.changeState(TRY(this->nextState()));
 
-    return Ok(HandleStatus::kDone);
+    return Ok(kHandleDone);
 }
 
 Result<http::RequestReader::IState *, error::AppError> http::ReadingHeadersState::nextState() const {
diff --git a/src/lib/http/request/reader/reading_request_line_state.cpp b/src/lib/http/request/reader/reading_request_line_state.cpp
index ccd801d4..4b8e8cce 100644
--- a/src/lib/http/request/reader/reading_request_line_state.cpp
+++ b/src/lib/http/request/reader/reading_request_line_state.cpp
@@ -9,11 +9,11 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError>
 http::ReadingRequestLineState::handle(ReadBuffer &readBuf) {
     const Option<std::string> reqLine = TRY(getLine(readBuf));
     if (reqLine.isNone()) {
-        return Ok(HandleStatus::kSuspend);
+        return Ok(kSuspend);
     }
 
     ctx_.setRequestLine(reqLine.unwrap());
     ctx_.changeState(new ReadingHeadersState(ctx_));
 
-    return Ok(HandleStatus::kDone);
+    return Ok(kHandleDone);
 }
diff --git a/src/lib/http/request/reader/request_reader.cpp b/src/lib/http/request/reader/request_reader.cpp
index 527fc517..0994d808 100644
--- a/src/lib/http/request/reader/request_reader.cpp
+++ b/src/lib/http/request/reader/request_reader.cpp
@@ -46,7 +46,7 @@ Result<http::RequestReader::IState::HandleStatus, error::AppError>
 http::RequestReader::ReadContext::handle(ReadBuffer &readBuf) const {
     if (state_ == NULL) {
         // 終了状態で呼び出したら、何もしない
-        return Ok(IState::kDone);
+        return Ok(IState::kHandleDone);
     }
     return state_->handle(readBuf);
 }
diff --git a/src/lib/http/request/reader/request_reader.hpp b/src/lib/http/request/reader/request_reader.hpp
index 9e9f4eda..4dedc8e4 100644
--- a/src/lib/http/request/reader/request_reader.hpp
+++ b/src/lib/http/request/reader/request_reader.hpp
@@ -26,7 +26,7 @@ namespace http {
     public:
         class IState {
         public:
-            enum HandleStatus { kSuspend, kDone };
+            enum HandleStatus { kSuspend, kHandleDone };
             virtual ~IState();
             virtual Result<HandleStatus, error::AppError> handle(ReadBuffer &readBuf) = 0;
         };
diff --git a/src/lib/http/response/response_builder.cpp b/src/lib/http/response/response_builder.cpp
index 2573ebe7..c7edfba5 100644
--- a/src/lib/http/response/response_builder.cpp
+++ b/src/lib/http/response/response_builder.cpp
@@ -45,7 +45,7 @@ namespace http {
     }
 
     ResponseBuilder &ResponseBuilder::file(const std::string &path, HttpStatusCode status) {
-        std::ifstream ifs(path);
+        std::ifstream ifs(path.c_str());
         if (!ifs.is_open()) {
             return this->status(kStatusNotFound);
         }
diff --git a/src/lib/transport/address.hpp b/src/lib/transport/address.hpp
index 47d94e5f..18bfa464 100644
--- a/src/lib/transport/address.hpp
+++ b/src/lib/transport/address.hpp
@@ -14,7 +14,7 @@ class Address {
 
 private:
     std::string ip_;
-    unsigned short port_{};
+    unsigned short port_;
 };
 
 #endif
diff --git a/src/lib/utils/auto_deleter.hpp b/src/lib/utils/auto_deleter.hpp
index 08b4eacf..f4499979 100644
--- a/src/lib/utils/auto_deleter.hpp
+++ b/src/lib/utils/auto_deleter.hpp
@@ -9,7 +9,7 @@
 template <typename T>
 class AutoDeleter : public NonCopyable {
 public:
-    using Deleter = void (*)(T *);
+    typedef void (*Deleter)(T *);
 
     explicit AutoDeleter(T *ptr = NULL, const Deleter deleter = NULL) : ptr_(ptr), deleter_(deleter) {}
 
diff --git a/src/lib/utils/ref.hpp b/src/lib/utils/ref.hpp
index a8d6422d..f39b18bc 100644
--- a/src/lib/utils/ref.hpp
+++ b/src/lib/utils/ref.hpp
@@ -1,7 +1,6 @@
 #ifndef SRC_LIB_UTILS_REF_HPP
 #define SRC_LIB_UTILS_REF_HPP
 
-#include <type_traits>
 
 // C++11 の std::reference_wrapper を再現
 template <typename T>
@@ -15,12 +14,6 @@ class Ref {
 
     Ref(const Ref &ref) : ptr_(ref.ptr_) {}
 
-    // Ref<T> -> Ref<const T> を可能にする
-    // TODO: C++11 の機能を使っているので、提出時に修正
-    template <typename U = T>
-    // ReSharper disable once CppNonExplicitConvertingConstructor
-    Ref(const Ref<typename std::remove_const<U>::type> &ref) : ptr_(&ref.get()) {} // NOLINT(*-explicit-constructor)
-
     ~Ref() {
         // あくまで reference なので、delete しない
     }
@@ -46,6 +39,10 @@ class Ref {
         return *ptr_;
     }
 
+    Ref<const T> toConst() const {
+        return Ref<const T>(*ptr_);
+    }
+
 private:
     T *ptr_;
 };
diff --git a/src/lib/utils/types/either.hpp b/src/lib/utils/types/either.hpp
index 6fe10d39..d829f9bd 100644
--- a/src/lib/utils/types/either.hpp
+++ b/src/lib/utils/types/either.hpp
@@ -2,7 +2,7 @@
 #define EITHER_HPP
 
 #include <stdexcept>
-#include <type_traits>
+
 
 namespace types {
     template <class T>
@@ -12,8 +12,7 @@ namespace types {
 
         // コピーコンストラクタではない
         // Either<T, R>(Left<U>) のコンストラクタで Left<U> -> Left<T> に変換するために必要
-        // TODO: 提出時に消す
-        template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+        template <class U>
         explicit Left(Left<U> &other) : val_(other.val()) {}
 
         Left(const Left &other) : val_(other.val_) {}
@@ -50,8 +49,7 @@ namespace types {
 
         // コピーコンストラクタではない
         // Either<T, R>(Right<U>) のコンストラクタで Right<U> -> Right<T> に変換するために必要
-        // TODO: 提出時に消す
-        template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+        template <class U>
         explicit Right(Right<U> &other) : val_(other.val()) {}
 
         Right(const Right &other) : val_(other.val_) {}
@@ -114,14 +112,12 @@ class Either {
      * Either<std::string, E> r2 = Left("hello");
      */
     // U -> T に変換可能であるという制約を付けないと、IDE 上でエラーが出ない (コンパイル時に出る)
-    // TODO: std::is_convertible などは C++11 以降なので、提出時に消す
-    template <class U, typename = typename std::enable_if<std::is_convertible<U, L>::value>::type>
+    template <class U>
     // NOLINTNEXTLINE(google-explicit-constructor)
     Either(types::Left<U> left) : left_(new types::Left<L>(left)), right_(NULL) {}
 
     // either.map(Some<L>) の型 Either<Some<L>, E> から Either<Option<L>, E> に変換するために必要
-    // TODO: 提出時に消す
-    template <class U, typename = typename std::enable_if<std::is_convertible<U, L>::value>::type>
+    template <class U>
     // NOLINTNEXTLINE(google-explicit-constructor)
     Either(const Either<U, R> &other) {
         if (other.isLeft()) {
diff --git a/src/lib/utils/types/option.hpp b/src/lib/utils/types/option.hpp
index 4991f3c1..1ffa14c1 100644
--- a/src/lib/utils/types/option.hpp
+++ b/src/lib/utils/types/option.hpp
@@ -95,9 +95,7 @@ class Option {
     explicit Option(types::Some<T> *some) : some_(some) {}
 
     // Option<std::string> op = Some("hello"); のように注釈を不要にするために必要
-    // TODO: 提出時に消す
-    // ReSharper disable once CppUseTypeTraitAlias
-    template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+    template <class U>
     // NOLINTNEXTLINE(google-explicit-constructor)
     Option(types::Some<U> some) : some_(new types::Some<T>(some.val())) {}
 
diff --git a/src/lib/utils/types/result.hpp b/src/lib/utils/types/result.hpp
index 6e38e2dc..1d817bae 100644
--- a/src/lib/utils/types/result.hpp
+++ b/src/lib/utils/types/result.hpp
@@ -30,8 +30,7 @@ namespace types {
 
         // コピーコンストラクタではない
         // Result<T, E>(Ok<U>) のコンストラクタで Ok<U> -> Ok<T> に変換するために必要
-        // TODO: 提出時に消す
-        template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+        template <class U>
         explicit Ok(Ok<U> &other) : val_(other.val()) {}
 
         Ok(const Ok &other) : val_(other.val_) {}
@@ -154,14 +153,12 @@ class Result {
      * Result<std::string, E> r2 = Ok("hello");
      */
     // U -> T に変換可能であるという制約を付けないと、IDE 上でエラーが出ない (コンパイル時に出る)
-    // TODO: std::is_convertible などは C++11 以降なので、提出時に消す
-    template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+    template <class U>
     // NOLINTNEXTLINE(google-explicit-constructor)
     Result(types::Ok<U> ok) : ok_(new types::Ok<T>(ok)), err_(NULL) {}
 
     // result.map(Some<T>) の型 Result<Some<T>, E> から Result<Option<T>, E> に変換するために必要
-    // TODO: 提出時に消す
-    template <class U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type>
+    template <class U>
     // NOLINTNEXTLINE(google-explicit-constructor)
     Result(const Result<U, E> &other) {
         if (other.isOk()) {
diff --git a/src/lib/utils/types/try.hpp b/src/lib/utils/types/try.hpp
index a3d969f2..9d86832b 100644
--- a/src/lib/utils/types/try.hpp
+++ b/src/lib/utils/types/try.hpp
@@ -14,19 +14,18 @@ types::None tryDefault(const Option<T> &) {
     return None;
 }
 
-// typeof(expr) は式を評価しないので、全体として一回だけ expr が評価される
-#define TRY(expr)                                                                \
-    ({                                                                           \
-        typeof(expr) e = (expr); /* NOLINT(*-unnecessary-copy-initialization) */ \
-        if (!(e).canUnwrap()) return tryDefault(e);                              \
-        (e).unwrap();                                                            \
+#define TRY(expr)                                                                  \
+    ({                                                                             \
+        __typeof(expr) e = (expr); /* NOLINT(*-unnecessary-copy-initialization) */ \
+        if (!(e).canUnwrap()) return tryDefault(e);                                \
+        (e).unwrap();                                                              \
     })
 
-#define TRY_OR(expr, defaultValue)                                               \
-    ({                                                                           \
-        typeof(expr) e = (expr); /* NOLINT(*-unnecessary-copy-initialization) */ \
-        if (!(e).canUnwrap()) return defaultValue;                               \
-        (e).unwrap();                                                            \
+#define TRY_OR(expr, defaultValue)                                                 \
+    ({                                                                             \
+        __typeof(expr) e = (expr); /* NOLINT(*-unnecessary-copy-initialization) */ \
+        if (!(e).canUnwrap()) return defaultValue;                                 \
+        (e).unwrap();                                                              \
     })
 
 #endif