constable.lua

-- constable.lua

function BuildConstantsTable(kvpairs)
	local t_Const={}
	
	for k,v in next,kvpairs,nil do
		t_Const[k]=v
	end
	
	local consts = {}
	
	setmetatable(consts,
		{
			constants = t_Const;
			
			__index=function(table, key)
				return getmetatable(table).constants[key]
			end;
			
			__newindex=function(table, key)
				error("Attempt to rewrite constant "..key)
			end;
		} )
	
	return consts
end

Keys = BuildConstantsTable({KEY_UP=5,KEY_DOWN=10,KEY_LEFT=20,KEY_RIGHT=40})

print(Keys.KEY_UP)
Keys.KEY_UP=20
print(Keys.KEY_UP)