diff --git a/include/rexy/compat/cpp17/cx/string.hpp b/include/rexy/compat/cpp17/cx/string.hpp
new file mode 100644
index 0000000..342328a
--- /dev/null
+++ b/include/rexy/compat/cpp17/cx/string.hpp
@@ -0,0 +1,44 @@
+/**
+	This file is a part of rexy's general purpose library
+	Copyright (C) 2022 rexy712
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef REXY_COMPAT_CPP17_CX_STRING_HPP
+#define REXY_COMPAT_CPP17_CX_STRING_HPP
+
+#include "../../../string_base.hpp" //string_cat_expr
+#include "../../../string_view.hpp" //string_view
+#include <utility> //forward
+#include <type_traits> //enable_if
+
+namespace rexy::cx{
+
+	template<class Str1, class Str2, std::enable_if_t<is_cx_string<Str1,Str2>::value,int> = 0>
+	constexpr auto operator+(Str1&& l, Str2&& r)noexcept{
+		return string_cat_expr(std::forward<Str1>(l), std::forward<Str2>(r));
+	}
+	template<class Str1, std::enable_if_t<is_cx_string<Str1>::value,int> = 0>
+	constexpr auto operator+(Str1&& l, const char* r)noexcept{
+		return string_cat_expr(std::forward<Str1>(l), rexy::basic_string_view<char>(r));
+	}
+	template<class Str1, std::enable_if_t<is_cx_string<Str1>::value,int> = 0>
+	constexpr auto operator+(const char* l, Str1&& r)noexcept{
+		return string_cat_expr(rexy::basic_string_view<char>(l), std::forward<Str1>(r));
+	}
+
+}
+
+#endif
diff --git a/include/rexy/compat/cpp20/cx/string.hpp b/include/rexy/compat/cpp20/cx/string.hpp
new file mode 100644
index 0000000..47db615
--- /dev/null
+++ b/include/rexy/compat/cpp20/cx/string.hpp
@@ -0,0 +1,46 @@
+/**
+	This file is a part of rexy's general purpose library
+	Copyright (C) 2022 rexy712
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef REXY_COMPAT_CPP20_CX_STRING_HPP
+#define REXY_COMPAT_CPP20_CX_STRING_HPP
+
+#include "../../../string_base.hpp" //string_cat_expr
+#include "../../../string_view.hpp" //string_view
+#include <utility> //forward
+
+namespace rexy{
+	template<class T>
+	concept CxString = cx::is_cx_string<T>::value;
+}
+namespace rexy::cx{
+	template<CxString Str1, CxString Str2>
+	constexpr auto operator+(Str1&& l, Str2&& r)noexcept{
+		return string_cat_expr(std::forward<Str1>(l), std::forward<Str2>(r));
+	}
+	template<CxString Str1>
+	constexpr auto operator+(Str1&& l, const char* r)noexcept{
+		return string_cat_expr(std::forward<Str1>(l), rexy::basic_string_view<char>(r));
+	}
+	template<CxString Str1>
+	constexpr auto operator+(const char* l, Str1&& r)noexcept{
+		return string_cat_expr(rexy::basic_string_view<char>(l), std::forward<Str1>(r));
+	}
+
+}
+
+#endif
diff --git a/include/rexy/cx/string.hpp b/include/rexy/cx/string.hpp
index 6029037..cbac8c8 100644
--- a/include/rexy/cx/string.hpp
+++ b/include/rexy/cx/string.hpp
@@ -1,6 +1,6 @@
 /**
 	This file is a part of rexy's general purpose library
-	Copyright (C) 2020 rexy712
+	Copyright (C) 2020-2022 rexy712
 
 	This program is free software: you can redistribute it and/or modify
 	it under the terms of the GNU General Public License as published by
@@ -19,15 +19,17 @@
 #ifndef REXY_CX_STRING_HPP
 #define REXY_CX_STRING_HPP
 
+#include <cstddef> //ptrdiff_t, size_t
+
 namespace rexy::cx{
-	template<size_t N, class Char>
+	template<std::size_t N, class Char>
 	class string;
 }
 
-#include "../string_base.hpp"
-#include "../utility.hpp"
-#include <type_traits>
-#include <cstddef> //ptrdiff_t, size_t
+#include "../string_base.hpp" //string_cat_expr
+#include "../utility.hpp" //strlen
+#include "../detail/string_appender.hpp"
+#include <type_traits> //nothrow_invocable, integral_constant, declval, remove_cvref_t
 
 #include "../compat/standard.hpp"
 
@@ -42,8 +44,8 @@ namespace rexy::cx{
 	{
 	public:
 		using value_type = Char;
-		using size_type = size_t;
-		using difference_type = ptrdiff_t;
+		using size_type = std::size_t;
+		using difference_type = std::ptrdiff_t;
 		using pointer = value_type*;
 		using const_pointer = const value_type*;
 		using reference = value_type&;
@@ -52,15 +54,15 @@ namespace rexy::cx{
 		using const_iterator = const_pointer;
 
 	public:
-		static constexpr size_t max_size = N;
-	private:
+		static constexpr std::size_t max_size = N;
+	public:
 		value_type m_data[N] = {};
 		size_type m_length = 0;
 
 	public:
 		constexpr string(void) = default;
 		template<size_type M>
-		constexpr string(const char(&data)[M])noexcept:
+		constexpr string(const value_type(&data)[M])noexcept:
 			m_length(M)
 		{
 			static_assert(M <= N);
@@ -69,7 +71,7 @@ namespace rexy::cx{
 			}
 		}
 		constexpr string(const_pointer data)noexcept:
-			m_length(strlen(data))
+			m_length(rexy::strlen(data))
 		{
 			for(size_type i = 0;i < m_length;++i){
 				m_data[i] = data[i];
@@ -103,7 +105,7 @@ namespace rexy::cx{
 		REXY_CPP20_CONSTEXPR ~string(void)noexcept = default;
 
 		constexpr string& operator=(const_pointer c)noexcept{
-			m_length = strlen(c);
+			m_length = rexy::strlen(c);
 			for(size_type i = 0;i < m_length;++i){
 				m_data[i] = c[i];
 			}
@@ -113,44 +115,34 @@ namespace rexy::cx{
 		constexpr string& operator=(string&&)noexcept = default;
 
 
-		constexpr size_type length(void)const noexcept{
-			return m_length;
-		}
-		constexpr size_type capacity(void)const noexcept{
-			return max_size;
-		}
-		constexpr pointer c_str(void)noexcept{
-			return m_data;
-		}
-		constexpr const_pointer c_str(void)const noexcept{
-			return m_data;
-		}
-		constexpr pointer get(void)noexcept{
-			return m_data;
-		}
-		constexpr const_pointer get(void)const noexcept{
-			return m_data;
-		}
-		constexpr operator pointer(void)noexcept{
-			return m_data;
-		}
-		constexpr operator const_pointer(void)const noexcept{
-			return m_data;
-		}
+		constexpr size_type length(void)const noexcept
+			{return m_length;}
+		constexpr size_type capacity(void)const noexcept
+			{return max_size;}
+		constexpr pointer c_str(void)noexcept
+			{return m_data;}
+		constexpr const_pointer c_str(void)const noexcept
+			{return m_data;}
+		constexpr pointer get(void)noexcept
+			{return m_data;}
+		constexpr const_pointer get(void)const noexcept
+			{return m_data;}
+		constexpr operator pointer(void)noexcept
+			{return m_data;}
+		constexpr operator const_pointer(void)const noexcept
+			{return m_data;}
 
-		constexpr bool valid(void)const noexcept{
-			return m_length > 0;
-		}
-		constexpr reference operator[](size_type i)noexcept{
-			return m_data[i];
-		}
-		constexpr const_reference operator[](size_type i)const noexcept{
-			return m_data[i];
-		}
+		constexpr bool valid(void)const noexcept
+			{return m_length > 0;}
+		constexpr reference operator[](size_type i)noexcept
+			{return m_data[i];}
+		constexpr const_reference operator[](size_type i)const noexcept
+			{return m_data[i];}
 
 		constexpr bool resize(size_type i)noexcept{
-			if(i >= capacity())
+			if(i >= capacity()){
 				return false;
+			}
 			m_length = i;
 			m_data[m_length] = 0;
 			return true;
@@ -161,46 +153,32 @@ namespace rexy::cx{
 				m_data[m_length++] = data[i];
 			}
 		}
-		constexpr void append(const_pointer data)noexcept{
-			append(data, strlen(data));
-		}
-		constexpr void append(const string& s)noexcept{
-			append(s.get(), s.length());
-		}
-		constexpr void append(const rexy::basic_string_view<value_type>& s)noexcept{
-			append(s.get(), s.length());
-		}
+		constexpr void append(const_pointer data)noexcept
+			{append(data, rexy::strlen(data));}
+		constexpr void append(const string& s)noexcept
+			{append(s.get(), s.length());}
+		constexpr void append(const rexy::basic_string_view<value_type>& s)noexcept
+			{append(s.get(), s.length());}
+	};
+	template<class Char, std::size_t N>
+	string(const Char(&data)[N]) -> string<N, Char>;
+
+	template<class... Ts>
+	struct is_cx_string{
+		template<class Char, std::size_t N>
+		static std::true_type check(cx::string<N,Char>);
+		static std::false_type check(...);
+		static constexpr bool value = (decltype(check(std::declval<std::remove_cvref_t<Ts>>()))::value && ...);
 	};
 
-	namespace detail{
-		template<class T>
-		struct is_cx_string_helper{
-			static constexpr bool value = false;
-		};
-		template<size_t N, class Char>
-		struct is_cx_string_helper<cx::string<N,Char>>{
-			static constexpr bool value = true;
-		};
-		template<class... Ts>
-		struct is_cx_string{
-			static constexpr bool value = (is_cx_string_helper<std::decay_t<Ts>>::value && ...);
-		};
-	}
-
-	template<class Str1, class Str2, std::enable_if_t<detail::is_cx_string<Str1,Str2>::value,int> = 0>
-	constexpr auto operator+(Str1&& l, Str2&& r)noexcept{
-		return string_cat_expr(std::forward<Str1>(l), std::forward<Str2>(r));
-	}
-	template<class Str1, std::enable_if_t<detail::is_cx_string<Str1>::value,int> = 0>
-	constexpr auto operator+(Str1&& l, const char* r)noexcept{
-		return string_cat_expr(std::forward<Str1>(l), rexy::basic_string_view<char>(r));
-	}
-	template<class Str1, std::enable_if_t<detail::is_cx_string<Str1>::value,int> = 0>
-	constexpr auto operator+(const char* l, Str1&& r)noexcept{
-		return string_cat_expr(rexy::basic_string_view<char>(l), std::forward<Str1>(r));
-	}
 }
 
+#ifdef __cpp_concepts
+	#include "../compat/cpp20/cx/string.hpp"
+#else //__cpp_concepts
+	#include "../compat/cpp17/cx/string.hpp"
+#endif //__cpp_concepts
+
 #ifdef REXY_CX_HASH_HPP
 #include "cx_string_hash.hpp"
 #endif