Case with when conditions

local Tiger = {}
Tiger.__index = Tiger

function Tiger.new(age)
  return setmetatable({age = age}, Tiger)
end

-- Every branch has its own condition
local function describe(value)
  local kind = type(value)
  -- The type test goes first: it guards the rest
  if kind == "number" and value > 1000000 then
    return "Big number"
  elseif kind == "string" and #value < 256 then
    return "Short string"
  elseif getmetatable(value) == Tiger
         and value.age > 12 then
    return "Old tiger"
  else
    return "Unknown type"
  end
end

local old = describe(Tiger.new(15))
-- old = Old tiger

-- The condition fails: the next branch is tried
local young = describe(Tiger.new(5))
-- young = Unknown type

local big = describe(2000000)
-- big = Big number
local small = describe(42)
-- small = Unknown type
local text = describe("test")
-- text = Short string

print("old = " .. old)
print("young = " .. young)
print("big = " .. big)
print("small = " .. small)
print("text = " .. text)