util/TemplateString: new utility library

Makefile.am

@@ -511,6 +511,7 @@ libutil_a_SOURCES = \
 	src/util/FormatString.cxx src/util/FormatString.hxx \
 	src/util/Tokenizer.cxx src/util/Tokenizer.hxx \
 	src/util/TextFile.hxx \
+	src/util/TemplateString.hxx \
 	src/util/TimeParser.cxx src/util/TimeParser.hxx \
 	src/util/UriUtil.cxx src/util/UriUtil.hxx \
 	src/util/Manual.hxx \

src/util/TemplateString.hxx

@@ -0,0 +1,126 @@
+/*
+ * Copyright (C) 2015-2016 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef TEMPLATE_STRING_HXX
+#define TEMPLATE_STRING_HXX
+
+#include <stddef.h>
+
+namespace TemplateString {
+	/**
+	 * Construct a null-terminated string from a list of chars.
+	 */
+	template<char... _value>
+	struct Construct {
+		static constexpr char value[] = {_value..., 0};
+		static constexpr size_t size = sizeof...(_value);
+	};
+
+	template<char... _value>
+	constexpr char Construct<_value...>::value[];
+
+	/**
+	 * An empty string.
+	 */
+	struct Empty : Construct<> {};
+
+	/**
+	 * A string consisting of a single character.
+	 */
+	template<char ch>
+	struct CharAsString : Construct<ch> {};
+
+	/**
+	 * Invoke #F, pass all characters in #src from #i to #length
+	 * as variadic arguments.
+	 */
+	template<template<char...> class F,
+		 const char *src, size_t length, size_t i,
+		 char... _value>
+	struct VariadicChars : VariadicChars<F, src, length - 1, i + 1, _value..., src[i]> {
+		static_assert(length > 0, "Wrong length");
+	};
+
+	template<template<char...> class F,
+		 const char *src, size_t length,
+		 char... _value>
+	struct VariadicChars<F, src, 0, length, _value...> : F<_value...> {};
+
+	/**
+	 * Like #VariadicChars, but pass an additional argument to #F.
+	 */
+	template<template<typename Arg, char...> class F, typename Arg,
+		 const char *src, size_t length, size_t i,
+		 char... _value>
+	struct VariadicChars1 : VariadicChars1<F, Arg,
+					       src, length - 1, i + 1, _value..., src[i]> {
+		static_assert(length > 0, "Wrong length");
+	};
+
+	template<template<typename Arg, char...> class F, typename Arg,
+		 const char *src, size_t length,
+		 char... _value>
+	struct VariadicChars1<F, Arg, src, 0, length, _value...> : F<Arg, _value...> {};
+
+	template<const char *src, size_t length, char... value>
+	struct _BuildString : VariadicChars<Construct, src, length, 0,
+					    value...> {};
+
+	template<char ch, typename S>
+	struct InsertBefore : _BuildString<S::value, S::size, ch> {};
+
+	/**
+	 * Concatenate several strings.
+	 */
+	template<typename... Args>
+	struct Concat;
+
+	template<typename First, typename Second, typename... Args>
+	struct _Concat : Concat<Concat<First, Second>, Args...> {};
+
+	template<typename... Args>
+	struct Concat : _Concat<Args...> {};
+
+	template<typename Second, char... _value>
+	struct _Concat2 : _BuildString<Second::value, Second::size,
+				      _value...> {};
+
+	template<typename First, typename Second>
+	struct Concat<First, Second>
+		:VariadicChars1<_Concat2, Second,
+				First::value, First::size, 0> {};
+
+	template<typename First>
+	struct Concat<First> : First {};
+
+	template<>
+	struct Concat<> : Empty {};
+};
+
+#endif