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1-- Class.lua
2-- Compatible with Lua 5.1 (not 5.0).
3--
4-- Modified to use a metatable to reference base objects instead
5-- or performing shallow copies. This means smaller classes that
6-- are a bit more dynamic at the expence of some performance.
7
8-- NOTE, this class definition is ONLY defined for the current environment, NOT the _G environment so it is totally safe to use with other plugins, even those that depend on older Turbine samples
9class = function( base )
10	if ( base ~= nil ) then
11		local baseType = type( base );
12
13		if ( baseType ~= 'table' ) then
14			error( "Base class is not a table. Base class was a " .. baseType );
15		end
16	end
17
18	-- The class definition table. Contains all of the actual class
19	-- methods, constructor, and an IsA function automatically
20	-- provided.
21	local c  = { };
22
23	c.base = base;
24	c.IsA = function( self, klass )
25		local m = getmetatable( self );
26		
27		while m do 
28			if m == klass then
29				return true;
30			end
31			
32			m = m.base;
33		end
34		
35		return false;
36	end
37
38	-- The class definition metatable. This is used to hook up
39	-- base classes and then to register a call handler that is
40	-- used to construct new instances of the class.
41	local mt = { };
42	mt.__index = base;
43
44	mt.__call = function( class_tbl, ... )
45		if ( class_tbl.Abstract ) then
46			error "Abstract class cannot be constructed.";
47		end
48
49		-- Create the new class instance.
50		local instance = { };
51		setmetatable( instance, { __index = c } );
52		
53		-- Invoke the constructor if it exists.
54		if ( ( instance.Constructor ~= nil ) and ( type( instance.Constructor ) == 'function' ) ) then
55			instance:Constructor( ... );
56		end
57		
58		return instance;
59	end
60
61	setmetatable( c, mt );
62	return c;
63end