@@ -1,6 +1,5 @@
 import util;
-import output;
 
 ////////////////////////////////////////////////////////////////////////////////
 
 class Pos
@@ -8,12 +7,12 @@
 	public immutable int y, x;
 	mixin DeriveCreate;
 	mixin DeriveCompare;
 	mixin DeriveShow;
-	Pos clone() { return this; }
+	Pos clone() const { return new Pos(y, x); }
 
 @property:
-	Pos wait()  { return this; }
+	Pos wait()  { return this.clone(); }
 	Pos up()    { return new Pos(y+1, x); }
 	Pos down()  { return new Pos(y-1, x); }
 	Pos left()  { return new Pos(y, x-1); }
 	Pos right() { return new Pos(y, x+1); }
@@ -45,9 +44,9 @@
 	public immutable int base, pace;
 	mixin DeriveCreate;
 	mixin DeriveCompare;
 	mixin DeriveShow;
-	Water clone() { return this; }
+	Water clone() const { return new Water(base, pace); }
 
 	static load(string[string] params)
 	{
 		return new Water(
@@ -55,14 +54,14 @@
 			params.get("Flooding", "0").to!int()
 		);
 	}
 
-	int level(int number_of_update)
+	int level(int number_of_update) const
 	{
 		return pace ? base+(number_of_update/pace) : base;
 	}
 
-	int until_rise(int number_of_update)
+	int until_rise(int number_of_update) const
 	{
 		return pace ? pace-number_of_update%pace : int.max;
 	}
 }
@@ -103,10 +102,10 @@
 	Pos robot;
 	Pos lift;
 	int waterproof;
 
-	Map clone() { return new Map(this); }
-	this(Map m) {
+	Map clone() const { return new Map(this); }
+	this(const(Map) m) {
 		foreach(s; m.data)
 			this.data ~= s.dup;
 		this.robot = m.robot.clone();
 		this.lift = m.lift.clone();
@@ -139,20 +138,22 @@
 		int H() { return data.length; }
 		int W() { return data[0].length; }
 	}
 
-	char opIndex(int y, int x)
-	{
-		// Adjust coordinate to the spec. bottom-left is (1,1).
-		--y, --x;
-		if(y<0||H<=y||x<0||W<=x)
-			return '#';
-		return data[H-1-y][x];
-	}
+	const {
+		char opIndex(int y, int x)
+		{
+			// Adjust coordinate to the spec. bottom-left is (1,1).
+			--y, --x;
+			if(y<0||H<=y||x<0||W<=x)
+				return '#';
+			return data[H-1-y][x];
+		}
 
-	char opIndex(Pos p)
-	{
-		return this[p.y, p.x];
+		char opIndex(Pos p)
+		{
+			return this[p.y, p.x];
+		}
 	}
 
 	void opIndexAssign(char c, int y, int x)
 	{
@@ -301,34 +302,25 @@
 	this(string[] raw_data, string[string] params)
 	{
 		this.map = Map.load(raw_data, params);
 		this.water = Water.load(params);
-		this.output = new NilOutput;
 	}
 
-	Game clone() { return new Game(this); }
-	this(Game g) {
+	Game clone() const { return new Game(this); }
+	this(const(Game) g) {
 		map = g.map.clone();
 		water = g.water.clone();
-		output = new NilOutput;
 		turn = g.turn;
 		dead = g.dead;
 		lambda = g.lambda;
 		exit_bonus = g.exit_bonus;
 		under_water = g.under_water;
 	}
 
-	void set_output(Output o) { this.output = (o is null ? new NilOutput : o); }
-
 	void command(char c)
 	{
 		if(dead || cleared)
 			return;
-		scope(exit) {
-			if(dead || cleared)
-				output.flush();
-		}
-		this.output.command(c);
 
 		if(c == 'A')
 		{
 			exit_bonus = 1;
@@ -356,9 +348,8 @@
 	}
 
 	Map map;
 	Water water;
-	Output output;
 	int  turn = 0;
 	bool dead = false;
 	int  lambda = 0;
 	int  exit_bonus = 0;
@@ -365,9 +356,9 @@
 	int  under_water = 0;
 	// TODO: when adding members, take care of clone().
 	// TODO: fix this poor design.
 
-	@property {
+	@property const {
 		long score() { return lambda*25L*(1+exit_bonus) - turn; }
 		int water_level() { return water.level(turn); }
 		int water_until_rise() { return water.until_rise(turn); }
 		bool cleared() { return exit_bonus>0; }