use c++11 heterogeneous map lookups in config if possible.

this means that codes like cfg.child("abcd") or cfg["abcd"] won't create
a temporary std::string anymore. At least when cfg is const.

src/config.cpp

@@ -42,6 +42,24 @@ static lg::log_domain log_config("config");
 #define ERR_CF LOG_STREAM(err, log_config)
 #define DBG_CF LOG_STREAM(debug, log_config)
 
+
+#ifdef USE_HETEROGENOUS_LOOKUPS 
+struct config_simple_key
+{
+	const char* str;
+	int len;
+
+	friend bool operator<(const config_simple_key& l, const std::string& r)
+	{
+		return r.compare(0, r.size(), l.str, l.len) > 0;
+	}
+	friend bool operator<(const std::string& l, const config_simple_key& r)
+	{
+		return l.compare(0, l.size(), r.str, r.len) < 0;
+	}
+};
+#endif
+
 struct tconfig_implementation
 {
 	/**
@@ -653,14 +671,42 @@ config &config::child(const std::string& key, int n)
 	if (n < 0) n = i->second.size() + n;
 	if(size_t(n) < i->second.size()) {
 		return *i->second[n];
-	} else {
+	}
+	else {
+		DBG_CF << "The config object has only »" << i->second.size()
+			<< "« children named »" << key
+			<< "«; request for the index »" << n << "« cannot be honored.\n";
+
+		return invalid;
+	}
+}
+
+#ifdef USE_HETEROGENOUS_LOOKUPS
+config &config::child_impl(const char* key, int len, int n)
+{
+	check_valid();
+
+	const child_map::const_iterator i = children.find(config_simple_key{ key, len });
+	if (i == children.end()) {
+		DBG_CF << "The config object has no child named »"
+			<< key << "«.\n";
+
+		return invalid;
+	}
+
+	if (n < 0) n = i->second.size() + n;
+	if (size_t(n) < i->second.size()) {
+		return *i->second[n];
+	}
+	else {
 		DBG_CF << "The config object has only »" << i->second.size()
 			<< "« children named »" << key
 			<< "«; request for the index »" << n << "« cannot be honored.\n";
 
 		return invalid;
 	}
 }
+#endif
 
 config& config::child(const std::string& key, const std::string& parent)
 {
@@ -877,6 +923,18 @@ const config::attribute_value &config::operator[](const std::string &key) const
 	return empty_attribute;
 }
 
+#ifdef USE_HETEROGENOUS_LOOKUPS
+const config::attribute_value& config::get_attribute(const char* key, int len) const
+{
+	check_valid();
+
+	const attribute_map::const_iterator i = values.find(config_simple_key { key, len });
+	if (i != values.end()) return i->second;
+	static const attribute_value empty_attribute;
+	return empty_attribute;
+}
+
+#endif
 const config::attribute_value *config::get(const std::string &key) const
 {
 	check_valid();

src/config.hpp

@@ -50,6 +50,11 @@
 #include "exceptions.hpp"
 #include "tstring.hpp"
 
+ //TODO: enable for gcc 5.0 and clang 3.4
+#if defined(_MSC_VER) && _MSC_VER >= 1900
+# define USE_HETEROGENOUS_LOOKUPS
+#endif
+
 class config;
 class enum_tag;
 
@@ -99,7 +104,11 @@ class config
 	{ return this != &invalid; }
 
 	typedef std::vector<config*> child_list;
-	typedef std::map<std::string,child_list> child_map;
+	typedef std::map<std::string, child_list
+#ifdef USE_HETEROGENOUS_LOOKUPS
+		, std::less<>
+#endif
+	> child_map;
 
 	struct const_child_iterator;
 
@@ -357,7 +366,13 @@ class config
 		static const std::string s_true, s_false;
 	};
 
-	typedef std::map<std::string, attribute_value> attribute_map;
+	typedef std::map<
+		std::string
+		, attribute_value
+#ifdef USE_HETEROGENOUS_LOOKUPS
+		, std::less<>
+#endif
+	> attribute_map;
 	typedef attribute_map::value_type attribute;
 
 	struct const_attribute_iterator
@@ -415,6 +430,12 @@ class config
 	 */
 	config &child(const std::string& key, int n = 0);
 
+#ifdef USE_HETEROGENOUS_LOOKUPS
+	template<int N>
+	config &child(const char(&key)[N], int n = 0)
+	{ return child_impl(key, N - 1, n); }
+	config &child_impl(const char* key, int len, int n = 0);
+#endif
 	/**
 	 * Returns the nth child with the given @a key, or
 	 * a reference to an invalid config if there is none.
@@ -424,6 +445,11 @@ class config
 	const config &child(const std::string& key, int n = 0) const
 	{ return const_cast<config *>(this)->child(key, n); }
 
+#ifdef USE_HETEROGENOUS_LOOKUPS
+	template<int N>
+	const config &child(const char(&key)[N], int n = 0) const
+	{ return const_cast<config *>(this)->child_impl(key, N- 1, n); }
+#endif
 	/**
 	 * Returns a mandatory child node.
 	 *
@@ -478,6 +504,18 @@ class config
 	 */
 	const attribute_value &operator[](const std::string &key) const;
 
+#ifdef USE_HETEROGENOUS_LOOKUPS
+	/**
+	 * Returns a reference to the attribute with the given @a key
+	 * or to a dummy empty attribute if it does not exist.
+	 */
+	template<int N>
+	inline const attribute_value &operator[](const char (&key)[N]) const
+	{
+		//-1 for the terminating null character.
+		return get_attribute(key, N - 1);
+	}
+#endif
 	/**
 	 * Returns a pointer to the attribute with the given @a key
 	 * or nullptr if it does not exist.
@@ -683,6 +721,9 @@ class config
 	void swap(config& cfg);
 
 private:
+#ifdef USE_HETEROGENOUS_LOOKUPS
+	const attribute_value& get_attribute(const char* key, int len) const;
+#endif
 	/**
 	 * Removes the child at position @a pos of @a l.
 	 */