local vec3 = {
    x = 0,
    y = 0,
    z = 0,
    w = "Hello, metatables!"
}
vec3.__index = vec3
vec3.__call = function(self, x, y, z)
    local t = { x = x, y = y,  z = z }
    setmetatable(t, vec3)
    return t
end

vec3.__add = function(o1, o2)
    local v = vec3(o1.x + o2.x, o1.y + o2.y, o1.z + o2.z)
    return v
end

function vec3:print()
  print("(" .. self.x .. ", " .. self.y ..", " .. self.z .. ")")
end
setmetatable(vec3, vec3)

local v = vec3(12, 4.5, 3)
local v2 = vec3(4, 1, 5)

v:print()
v2:print()
local v3 = v + v2
v3:print()