local vec3 = {
    x = 0,
    y = 0,
    z = 0,
    w = "Hello, metatables!"
}
local vec3_mt = {
    __index = vec3
}
vec3_mt.__call = function(self, x, y, z)
    local t = { x = _x, y = y,  z = z }
    setmetatable(t, vec3_mt)
    return t
end

vec3_mt.__add = function(o1, o2)
    local v = vec3(o1.x + o2.x, o1.y + o2.y, o1.z + o2.z)
    return v
end
setmetatable(vec3, vec3_mt)

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

print(v.x .. " " .. v.y .. " " .. v.z)
print(v2.x .. " " .. v2.y .. " " .. v2.z)

local v3 = v + v2
print("\n" .. v3.x .. " " .. v3.y .. " " .. v3.z)