a4blank@10: -- class.lua
a4blank@10: -- taken from http://lua-users.org/wiki/SimpleLuaClasses
a4blank@10: -- Compatible with Lua 5.1 (not 5.0).
a4blank@10: function class(base, init)
a4blank@10:    local c = {}    -- a new class instance
a4blank@10:    if not init and type(base) == 'function' then
a4blank@10:       init = base
a4blank@10:       base = nil
a4blank@10:    elseif type(base) == 'table' then
a4blank@10:     -- our new class is a shallow copy of the base class!
a4blank@10:       for i,v in pairs(base) do
a4blank@10:          c[i] = v
a4blank@10:       end
a4blank@10:       c._base = base
a4blank@10:    end
a4blank@10:    -- the class will be the metatable for all its objects,
a4blank@10:    -- and they will look up their methods in it.
a4blank@10:    c.__index = c
a4blank@10: 
a4blank@10:    -- expose a constructor which can be called by <classname>(<args>)
a4blank@10:    local mt = {}
a4blank@10:    mt.__call = function(class_tbl, ...)
a4blank@10:    local obj = {}
a4blank@10:    setmetatable(obj,c)
a4blank@10:    if class_tbl.init then
a4blank@10:       class_tbl.init(obj,...)
a4blank@10:    else 
a4blank@10:       -- make sure that any stuff from the base class is initialized!
a4blank@10:       if base and base.init then
a4blank@10:       base.init(obj, ...)
a4blank@10:       end
a4blank@10:    end
a4blank@10:    return obj
a4blank@10:    end
a4blank@10:    c.init = init
a4blank@10:    c.is_a = function(self, klass)
a4blank@10:       local m = getmetatable(self)
a4blank@10:       while m do 
a4blank@10:          if m == klass then return true end
a4blank@10:          m = m._base
a4blank@10:       end
a4blank@10:       return false
a4blank@10:    end
a4blank@10:    setmetatable(c, mt)
a4blank@10:    return c
a4blank@10: end