diff --git a/src/config.hpp b/src/config.hpp
index 46bf7a3f831..f751b6abf50 100644
--- a/src/config.hpp
+++ b/src/config.hpp
@@ -42,6 +42,7 @@
 typedef std::map<std::string, t_string> string_map;
 
 class config;
+class vconfig;
 struct lua_State;
 
 bool operator==(const config &, const config &);
@@ -202,6 +203,7 @@ public:
 		friend std::ostream& operator<<(std::ostream &os, const attribute_value &v);
 		friend void luaW_pushscalar(lua_State *, const attribute_value &);
 		friend void write_key_val(std::ostream &, const std::string &, const attribute_value &, unsigned, std::string &);
+		friend class vconfig;
 	};
 
 	typedef std::map<std::string, attribute_value> attribute_map;
@@ -482,4 +484,11 @@ private:
 	std::vector<child_pos> ordered_children;
 };
 
+class variable_set
+{
+public:
+	virtual ~variable_set() {}
+	virtual config::attribute_value get_variable_const(const std::string &id) const = 0;
+};
+
 #endif
diff --git a/src/formula_string_utils.cpp b/src/formula_string_utils.cpp
index 237234ad277..12773549674 100644
--- a/src/formula_string_utils.cpp
+++ b/src/formula_string_utils.cpp
@@ -30,15 +30,14 @@ class string_map_variable_set : public variable_set
 public:
 	string_map_variable_set(const string_map& map) : map_(map) {};
 
-	virtual t_string get_variable_const (const std::string& key) const
+	virtual config::attribute_value get_variable_const(const std::string &key) const
 	{
+		config::attribute_value val;
 		const string_map::const_iterator itor = map_.find(key);
-		if (itor == map_.end()) {
-			return t_string();
-		} else {
-			return itor->second;
-		}
-	};
+		if (itor != map_.end())
+			val = itor->second;
+		return val;
+	}
 private:
 	const string_map& map_;
 
diff --git a/src/formula_string_utils.hpp b/src/formula_string_utils.hpp
index 8af6ecce65b..523fb6d1954 100644
--- a/src/formula_string_utils.hpp
+++ b/src/formula_string_utils.hpp
@@ -17,6 +17,7 @@
 #define FORMULA_STRING_UTILS_HPP_INCLUDED
 
 #include "serialization/string_utils.hpp"
+#include "config.hpp"
 
 namespace utils {
 
diff --git a/src/game_events.cpp b/src/game_events.cpp
index 7f38215003f..dfd6f6cc46c 100644
--- a/src/game_events.cpp
+++ b/src/game_events.cpp
@@ -408,20 +408,19 @@ namespace game_events {
 		foreach (const vconfig &values, variables)
 		{
 			const std::string name = values["name"];
-			std::string value = resources::state_of_game->get_variable_const(name);
-
-			const double num_value = atof(value.c_str());
+			config::attribute_value value = resources::state_of_game->get_variable_const(name);
+			double num_value = value.to_double();
 
 #define TEST_STR_ATTR(name, test) do { \
 			if (values.has_attribute(name)) { \
-				std::string attr_str = values[name].str(); \
+				config::attribute_value attr_str = values[name]; \
 				if (!(test)) return false; \
 			} \
 			} while (0)
 
 #define TEST_NUM_ATTR(name, test) do { \
 			if (values.has_attribute(name)) { \
-				double attr_num = atof(values[name].c_str()); \
+				double attr_num = values[name].to_double(); \
 				if (!(test)) return false; \
 			} \
 			} while (0)
@@ -434,11 +433,9 @@ namespace game_events {
 			TEST_NUM_ATTR("less_than",             num_value <  attr_num);
 			TEST_NUM_ATTR("greater_than_equal_to", num_value >= attr_num);
 			TEST_NUM_ATTR("less_than_equal_to",    num_value <= attr_num);
-			TEST_STR_ATTR("boolean_equals",
-				utils::string_bool(value) == utils::string_bool(attr_str));
-			TEST_STR_ATTR("boolean_not_equals",
-				utils::string_bool(value) != utils::string_bool(attr_str));
-			TEST_STR_ATTR("contains", value.find(attr_str) != std::string::npos);
+			TEST_STR_ATTR("boolean_equals",        value == attr_str);
+			TEST_STR_ATTR("boolean_not_equals",    value != attr_str);
+			TEST_STR_ATTR("contains", value.str().find(attr_str.str()) != std::string::npos);
 
 #undef TEST_STR_ATTR
 #undef TEST_NUM_ATTR
@@ -1805,7 +1802,7 @@ WML_HANDLER_FUNCTION(object, event_info, cfg)
 
 	if (u != resources::units->end() && (filter.null() || game_events::unit_matches_filter(*u, filter)))
 	{
-		text = cfg["description"];
+		text = cfg["description"].str();
 
 		u->add_modification("object", cfg.get_parsed_config());
 
@@ -1815,7 +1812,7 @@ WML_HANDLER_FUNCTION(object, event_info, cfg)
 		// Mark this item as used up.
 		used_items.insert(id);
 	} else {
-		text = cfg["cannot_use_message"];
+		text = cfg["cannot_use_message"].str();
 		command_type = "else";
 	}
 
@@ -2038,13 +2035,13 @@ WML_HANDLER_FUNCTION(set_menu_item, /*event_info*/, cfg)
 		mref = new wml_menu_item(id);
 	}
 	if(cfg.has_attribute("image")) {
-		mref->image = cfg["image"];
+		mref->image = cfg["image"].str();
 	}
 	if(cfg.has_attribute("description")) {
 		mref->description = cfg["description"];
 	}
 	if(cfg.has_attribute("needs_select")) {
-		mref->needs_select = utils::string_bool(cfg["needs_select"], false);
+		mref->needs_select = cfg["needs_select"].to_bool();
 	}
 	if(cfg.has_child("show_if")) {
 		mref->show_if = cfg.child("show_if").get_config();
@@ -2308,7 +2305,7 @@ WML_HANDLER_FUNCTION(endlevel, /*event_info*/, cfg)
 	end_level_data &data = resources::controller->get_end_level_data();
 
 	std::string result = cfg["result"];
-	data.custom_endlevel_music = cfg["music"];
+	data.custom_endlevel_music = cfg["music"].str();
 	data.carryover_report = utils::string_bool(cfg["carryover_report"], true);
 	data.prescenario_save = utils::string_bool(cfg["save"], true);
 	data.linger_mode = utils::string_bool(cfg["linger_mode"], true)
@@ -2542,7 +2539,7 @@ std::string get_image(const vconfig& cfg, unit_map::iterator speaker)
 
 		image::locator locator(image);
 		if(!locator.file_exists()) {
-			image = cfg["image"];
+			image = cfg["image"].str();
 		}
 	}
 	return image;
diff --git a/src/gamestatus.cpp b/src/gamestatus.cpp
index 392fa9cab82..8c04bdd9130 100644
--- a/src/gamestatus.cpp
+++ b/src/gamestatus.cpp
@@ -475,16 +475,17 @@ config::attribute_value &game_state::get_variable(const std::string& key)
 	return variable_info(key, true, variable_info::TYPE_SCALAR).as_scalar();
 }
 
-t_string game_state::get_variable_const(const std::string& key) const
+config::attribute_value game_state::get_variable_const(const std::string &key) const
 {
 	variable_info to_get(key, false, variable_info::TYPE_SCALAR);
-	if(!to_get.is_valid) {
-			config::attribute_value &to_return = temporaries[key];
-			if (key.size() > 7 && key.substr(key.size()-7) == ".length") {
-				// length is a special attribute, so guarantee its correctness
-				to_return = "0";
-			}
-			return to_return;
+	if (!to_get.is_valid)
+	{
+		config::attribute_value &to_return = temporaries[key];
+		if (key.size() > 7 && key.substr(key.size() - 7) == ".length") {
+			// length is a special attribute, so guarantee its correctness
+			to_return = 0;
+		}
+		return to_return;
 	}
 	return to_get.as_scalar();
 }
diff --git a/src/gamestatus.hpp b/src/gamestatus.hpp
index b5949d2ff43..57995c7b7a2 100644
--- a/src/gamestatus.hpp
+++ b/src/gamestatus.hpp
@@ -103,7 +103,7 @@ public:
 	// Variable access
 
 	config::attribute_value &get_variable(const std::string &varname);
-	virtual t_string get_variable_const(const std::string& varname) const;
+	virtual config::attribute_value get_variable_const(const std::string& varname) const;
 	config& get_variable_cfg(const std::string& varname);
 
 	void set_variable(const std::string& varname, const t_string& value);
diff --git a/src/gui/auxiliary/formula.hpp b/src/gui/auxiliary/formula.hpp
index f5c6b9330d2..1c1fd16022d 100644
--- a/src/gui/auxiliary/formula.hpp
+++ b/src/gui/auxiliary/formula.hpp
@@ -20,6 +20,7 @@
 #include "gui/widgets/helper.hpp"
 #include "serialization/string_utils.hpp"
 #include "util.hpp"
+#include "tstring.hpp"
 
 #include <boost/static_assert.hpp>
 
diff --git a/src/gui/dialogs/gamestate_inspector.cpp b/src/gui/dialogs/gamestate_inspector.cpp
index 8708b615639..2b649424c07 100644
--- a/src/gui/dialogs/gamestate_inspector.cpp
+++ b/src/gui/dialogs/gamestate_inspector.cpp
@@ -79,7 +79,7 @@ public:
 	model(const vconfig &c)
 		: cfg(c), name(), stuff_list(),stuff_types_list(),inspect(),inspector_name()
 	{
-		name = cfg["name"];
+		name = cfg["name"].str();
 	}
 
 	vconfig cfg;
diff --git a/src/scripting/lua.cpp b/src/scripting/lua.cpp
index 29e22aa1905..48919e30927 100644
--- a/src/scripting/lua.cpp
+++ b/src/scripting/lua.cpp
@@ -165,32 +165,6 @@ void luaW_pushscalar(lua_State *L, config::attribute_value const &v)
 	boost::apply_visitor(luaW_pushscalar_visitor(L), v.value);
 }
 
-/**
- * Converts a string into a Lua object pushed at the top of the stack.
- * Boolean ("yes"/"no") and numbers are detected and typed accordingly.
- */
-static void luaW_pushscalar(lua_State *L, t_string const &v)
-{
-	if (!v.translatable())
-	{
-		char *pe;
-		char const *pb = v.c_str();
-		double d = strtod(v.c_str(), &pe);
-		if (pe != pb && *pe == '\0')
-			lua_pushnumber(L, d);
-		else if (v == "yes")
-			lua_pushboolean(L, true);
-		else if (v == "no")
-			lua_pushboolean(L, false);
-		else
-			lua_pushstring(L, pb);
-	}
-	else
-	{
-		luaW_pushtstring(L, v);
-	}
-}
-
 /**
  * Returns true if the metatable of the object is the one found in the registry.
  */
diff --git a/src/serialization/preprocessor.cpp b/src/serialization/preprocessor.cpp
index 168edd60066..dcb6c828f32 100644
--- a/src/serialization/preprocessor.cpp
+++ b/src/serialization/preprocessor.cpp
@@ -335,7 +335,7 @@ std::string lineno_string(const std::string &lineno)
 
 void preprocessor_streambuf::error(const std::string& error_type, int l)
 {
-	utils::string_map i18n_symbols;
+	string_map i18n_symbols;
 	std::string position, error;
 	std::ostringstream pos;
 	pos << l << ' ' << location_;
diff --git a/src/serialization/string_utils.cpp b/src/serialization/string_utils.cpp
index 6979cc75478..3429ca163f3 100644
--- a/src/serialization/string_utils.cpp
+++ b/src/serialization/string_utils.cpp
@@ -30,10 +30,6 @@ static lg::log_domain log_engine("engine");
 #define ERR_GENERAL LOG_STREAM(err, lg::general)
 #define ERR_NG LOG_STREAM(err, log_engine)
 
-variable_set::~variable_set()
-{
-}
-
 namespace utils {
 
 bool isnewline(const char c)
diff --git a/src/serialization/string_utils.hpp b/src/serialization/string_utils.hpp
index b4ea2495b97..5fede712a1d 100644
--- a/src/serialization/string_utils.hpp
+++ b/src/serialization/string_utils.hpp
@@ -24,18 +24,9 @@
 #include <string>
 #include <vector>
 #include <boost/next_prior.hpp>
-#include "../tstring.hpp"
 
 #include "SDL_types.h"
 
-class variable_set
-{
-public:
-	virtual ~variable_set();
-
-	virtual t_string get_variable_const(const std::string& id) const = 0;
-};
-
 /** The type we use to represent Unicode strings. */
 typedef std::vector<wchar_t> wide_string;
 
@@ -44,6 +35,8 @@ typedef std::vector<Uint16> ucs2_string;
 typedef std::vector<Uint32> ucs4_string;
 typedef std::string utf8_string;
 
+class t_string;
+
 namespace utils {
 
 const std::string unicode_minus = "−";
diff --git a/src/storyscreen/part.cpp b/src/storyscreen/part.cpp
index 548b0747a57..f2743834448 100644
--- a/src/storyscreen/part.cpp
+++ b/src/storyscreen/part.cpp
@@ -142,19 +142,19 @@ void part::resolve_wml(const vconfig &cfg)
 	}
 
 	if(cfg.has_attribute("background")) {
-		background_file_ = cfg["background"];
+		background_file_ = cfg["background"].str();
 	}
 	if(cfg.has_attribute("scale_background")) {
-		scale_background_ = utils::string_bool(cfg["scale_background"], true);
+		scale_background_ = cfg["scale_background"].to_bool(true);
 	}
 	if(cfg.has_attribute("show_title")) {
-		show_title_ = utils::string_bool(cfg["show_title"]);
+		show_title_ = cfg["show_title"].to_bool();
 	}
 	if(cfg.has_attribute("story")) {
-		text_ = cfg["story"];
+		text_ = cfg["story"].str();
 	}
 	if(cfg.has_attribute("title")) {
-		text_title_ = cfg["title"];
+		text_title_ = cfg["title"].str();
 		if(!cfg.has_attribute("show_title")) {
 			show_title_ = true;
 		}
@@ -166,10 +166,10 @@ void part::resolve_wml(const vconfig &cfg)
 		title_alignment_ = string_title_align(cfg["title_alignment"]);
 	}
 	if(cfg.has_attribute("music")) {
-		music_ = cfg["music"];
+		music_ = cfg["music"].str();
 	}
 	if(cfg.has_attribute("sound")) {
-		sound_ = cfg["sound"];
+		sound_ = cfg["sound"].str();
 	}
 
 	// Execution flow/branching/[image]
diff --git a/src/text.cpp b/src/text.cpp
index d57efdf87e4..b6ba773f89c 100644
--- a/src/text.cpp
+++ b/src/text.cpp
@@ -21,6 +21,7 @@
 #include "gui/auxiliary/log.hpp"
 #include "font.hpp"
 #include "serialization/string_utils.hpp"
+#include "tstring.hpp"
 
 #include <cassert>
 #include <cstring>
diff --git a/src/unit.cpp b/src/unit.cpp
index e60825dbceb..2d379cdf4f2 100644
--- a/src/unit.cpp
+++ b/src/unit.cpp
@@ -1496,7 +1496,7 @@ bool unit::internal_matches_filter(const vconfig& cfg, const map_location& loc,
 
 	if (cfg.has_attribute("lua_function")) {
 		bool b = resources::lua_kernel->run_filter
-			(cfg["lua_function"].c_str(), *this);
+			(cfg["lua_function"].str().c_str(), *this);
 		if (!b) return false;
 	}
 
diff --git a/src/unit_display.cpp b/src/unit_display.cpp
index ffe176ea78f..49a30f9b722 100644
--- a/src/unit_display.cpp
+++ b/src/unit_display.cpp
@@ -557,7 +557,7 @@ void wml_animation_internal(unit_animator &animator, const vconfig &cfg, const m
 		if(cfg["red"].empty() && cfg["green"].empty() && cfg["blue"].empty()) {
 			text_color = display::rgb(0xff,0xff,0xff);
 		} else {
-			text_color = display::rgb(atoi(cfg["red"].c_str()),atoi(cfg["green"].c_str()),atoi(cfg["blue"].c_str()));
+			text_color = display::rgb(cfg["red"], cfg["green"], cfg["blue"]);
 		}
 		resources::screen->scroll_to_tile(u->get_location(), game_display::ONSCREEN, true, false);
 		vconfig t_filter = cfg.child("facing");
diff --git a/src/variable.cpp b/src/variable.cpp
index e148bab7efc..c092d2b78da 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -32,6 +32,8 @@
 #include "unit_map.hpp"
 #include "team.hpp"
 
+#include <boost/variant.hpp>
+
 static lg::log_domain log_engine("engine");
 #define LOG_NG LOG_STREAM(info, log_engine)
 #define WRN_NG LOG_STREAM(warn, log_engine)
@@ -346,12 +348,27 @@ bool vconfig::has_child(const std::string& key) const
 	return false;
 }
 
-const t_string vconfig::expand(const std::string& key) const
+struct vconfig_expand_visitor : boost::static_visitor<void>
 {
-	const t_string& val = (*cfg_)[key];
-	if(repos != NULL)
-		return utils::interpolate_variables_into_tstring(val, *repos);
-	return t_string(val);
+	config::attribute_value &result;
+	vconfig_expand_visitor(config::attribute_value &r): result(r) {}
+	template<typename T> void operator()(T const &) const {}
+	void operator()(const std::string &s) const
+	{
+		result = utils::interpolate_variables_into_string(s, *repos);
+	}
+	void operator()(const t_string &s) const
+	{
+		result = utils::interpolate_variables_into_tstring(s, *repos);
+	}
+};
+
+config::attribute_value vconfig::expand(const std::string &key) const
+{
+	config::attribute_value val = (*cfg_)[key];
+	if (repos)
+		boost::apply_visitor(vconfig_expand_visitor(val), val.value);
+	return val;
 }
 
 vconfig::all_children_iterator::all_children_iterator(const Itor &i, const config *cache_key)
diff --git a/src/variable.hpp b/src/variable.hpp
index 9c27b26e741..7517ea71063 100644
--- a/src/variable.hpp
+++ b/src/variable.hpp
@@ -69,8 +69,9 @@ public:
 	 * lifetime ends which causes UB. Instead use:
 	 * const std::string temp = vcfg["foo"];
 	 */
-	const t_string operator[](const std::string& key) const { return expand(key); }
-	const t_string expand(const std::string&) const; /** < Synonym for operator[] */
+	const config::attribute_value operator[](const std::string &key) const
+	{ return expand(key); }
+	config::attribute_value expand(const std::string&) const; /** < Synonym for operator[] */
 	bool has_attribute(const std::string& key) const { return cfg_->has_attribute(key); }
 	bool empty() const { return (null() || cfg_->empty()); }