a member variable (output: 0) Inheritance Lua supports using metatables to give Lua class inheritance. In this example, we allow vectors to have their values multiplied by a constant in a derived class. local Vector = {} Vector.__index = Vector function Vector:new(x, y, z) -- The constructor -- Here, self refers to whatever class's "new" -- method we call. In a derived class, self will -- be the derived class; in the Vector class, self -- will be Vector return setmetatable({x = x, y = y, z = z}, self) end function Vector:magnitude() -- Another method -- Reference the implicit object using self return math.sqrt(self.x^2 + self.y^2 + self.z^2) end -- Example of class inheritance local VectorMult = {} VectorMult.__index = VectorMult setmetatable(VectorMult, Vector) -- Make VectorMult a child of Vector function VectorMult:multiply(value) self.x = self.x * value self.y = self.y * value self.z = self.z * value return self end local vec = VectorMult:new(0, 1, 0) -- Create a vector print(vec:magnitude()) -- Call a method (output: 1) print(vec.y) -- Access a member variable (output: 1) vec:multiply(2) -- Multiply all components of vector by 2 print(vec.y) -- Access member again (output: 2) Lua also supports multiple inheritance; can either be a function or a table. Operator overloading can also be done; Lua metatables can have elements such as , , and so on. Implementation Lua programs are not interpreted directly from the textual Lua file, but are compiled into bytecode, which is then run on the Lua virtual machine. The compilation process is typically invisible to the user and is performed during run-time, especially when a JIT compiler is used, but it can be done offline in order to increase loading performance or reduce the memory footprint of the host environment by leaving out the compiler. Lua bytecode can also be produced and executed from within Lua, using the dump function from the string library and the load/loadstring/loadfile functions. Lua version 5.3.4 is implemented in approximately 24,000 lines of C code. Like most CPUs, and unlike most virtual machines (which are stack-based), the Lua VM is register-based, and therefore more closely resembles an actual hardware design. The register architecture both avoids excessive copying of values and reduces the total number of instructions per function. The virtual machine of Lua 5 is one of the first register-based pure VMs to have a wide use. Parrot and Android's Dalvik are two other