From 76f62be24b7e612b1f6880f9d7b0ddc07a8d38eb Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Sat, 18 Apr 2020 00:22:41 +0800
Subject: ...

---
 include/cru/common/format.hpp | 99 ++++++++++++++++++++++++++++---------------
 1 file changed, 64 insertions(+), 35 deletions(-)

(limited to 'include/cru/common/format.hpp')

diff --git a/include/cru/common/format.hpp b/include/cru/common/format.hpp
index 4405c8c5..4276880e 100644
--- a/include/cru/common/format.hpp
+++ b/include/cru/common/format.hpp
@@ -7,62 +7,91 @@
 
 namespace cru::util {
 namespace details {
-template <typename T>
+template <typename TChar>
 struct FormatTrait {};
 
 template <>
-struct FormatTrait<std::string_view> {
-  static constexpr std::string_view placeholder = "{}";
-  using ResultType = std::string;
+struct FormatTrait<char> {
+  using StringType = std::string;
+  using ViewType = std::string_view;
   using StreamType = std::stringstream;
+  static constexpr ViewType placeholder = "{}";
 };
 
 template <>
-struct FormatTrait<std::wstring_view> {
-  static constexpr std::wstring_view placeholder = L"{}";
-  using ResultType = std::wstring;
+struct FormatTrait<wchar_t> {
+  using StringType = std::wstring;
+  using ViewType = std::wstring_view;
   using StreamType = std::wstringstream;
+  static constexpr ViewType placeholder = L"{}";
+};
+}  // namespace details
+
+template <typename TFormatTrait, typename T>
+struct Formatter {
+  static typename TFormatTrait::StringType Format(const T& value) {
+    typename TFormatTrait::StreamType stream;
+    stream << value;
+    return stream.str();
+  }
 };
 
-template <typename TStringView>
-void FormatInternal(typename FormatTrait<TStringView>::StreamType& stream,
-                    const TStringView& string) {
-  const auto find_result = string.find(FormatTrait<TStringView>::placeholder);
-  if (find_result != TStringView::npos)
+namespace details {
+template <typename TString>
+void FormatInternal(TString& string) {
+  using Trait = FormatTrait<TString::value_type>;
+  constexpr const auto& placeholder = Trait::placeholder;
+
+  const auto find_result = string.find(placeholder);
+  if (find_result != TString::npos)
     throw std::invalid_argument("There is more placeholders than args.");
-  stream << string;
 }
 
-template <typename TStringView, typename T, typename... TRest>
-void FormatInternal(typename FormatTrait<TStringView>::StreamType& stream,
-                    const TStringView& string, const T& arg,
-                    const TRest&... args) {
-  const auto find_result = string.find(FormatTrait<TStringView>::placeholder);
-  if (find_result == TStringView::npos)
-    throw std::invalid_argument("There is less placeholders than args.");
-
-  stream << string.substr(0, find_result);
-  stream << arg;
+template <typename TString, typename T, typename... TRest>
+void FormatInternal(TString& string, const T& arg, const TRest&... args) {
+  using Trait = FormatTrait<TString::value_type>;
+  constexpr const auto& placeholder = Trait::placeholder;
 
-  FormatInternal(stream, string.substr(find_result + 2), args...);
-}
+  const auto find_result = string.find(placeholder);
+  if (find_result == TString::npos)
+    throw std::invalid_argument("There is less placeholders than args.");
 
-template <typename TStringView, typename... T>
-auto FormatTemplate(const TStringView& format, const T&... args) ->
-    typename FormatTrait<TStringView>::ResultType {
-  typename FormatTrait<TStringView>::StreamType stream;
-  FormatInternal(stream, format, args...);
-  return stream.str();
+  string.replace(find_result, 2, Formatter<Trait, T>::Format(arg));
+  FormatInternal<TString>(string, args...);
 }
 }  // namespace details
 
 template <typename... T>
-std::wstring Format(const std::wstring_view& format, const T&... args) {
-  return details::FormatTemplate(format, args...);
+std::wstring Format(std::wstring format, const T&... args) {
+  details::FormatInternal(format, args...);
+  return format;
 }
 
 template <typename... T>
-std::string Format(const std::string_view& format, const T&... args) {
-  return details::FormatTemplate(format, args...);
+std::string Format(std::string format, const T&... args) {
+  details::FormatInternal(format, args...);
+  return format;
+}
+
+// Why is two overloads below exist?
+// Because people should be able to pass string_view instance as format.
+// However, the two overloads above do not accept string_view as format due to
+// conversion from string_view to string is explicit.
+//
+// Why not just overload but SFINAE?
+// Because I want to make two overloads below worse than the two ones above.
+// Otherwise it will be ambiguous when pass const char* as format.
+//
+
+template <typename T, typename... TArgs>
+auto Format(T format, const TArgs&... args)
+    -> std::enable_if_t<std::is_same_v<T, std::wstring_view>, std::wstring> {
+  return Format(std::wstring{format}, args...);
+}
+
+template <typename T, typename... TArgs>
+auto Format(T format, const TArgs&... args)
+    -> std::enable_if_t<std::is_same_v<T, std::string_view>, std::string> {
+  return Format(std::string{format}, args...);
 }
 }  // namespace cru::util
-- 
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