Class concept for lua 5.1

class.lua

-- implementation

function class(i)
  local c = {fields={},field_types={}}
  assert(type(i)=="table","class expects a table input.")
  for type_name,default_value in pairs(i) do
    local t,n = nil,nil
    string.gsub(
      type_name,
      "(%l*)(%l*)",
      function(i)
        if i ~= "" then
          if t then
            n = i
          else
            t = i
          end
        end
      end
    )
    assert(t ~= nil and n ~= nil,"`"..type_name.."` is not valid.")
    c.fields[n] = default_value
    c.field_types[n] = t
  end

  local mt = {
    __newindex = function(n,v)
print('newindex',n,v)
      assert(c.fields[n],
        "Field `"..n.."` does not exist in class")
      assert(c.field_types[n] == type(v),
        "Field `"..n.."` expects `"..c[index].."`, got `"..type(v).."`.")
      c[n] = v
    end,
    __call = c.new
  }

  c.new = function(init)
    local self = {}
    for i,v in pairs(c.fields) do
      print("init",i,v)
    end
    setmetatable(self,mt)
    return self
  end
  setmetatable(c,{
    __call = c.new
  })

  return c
end

-- sample usage

local barclass = class{}

local fooclass = class{
--  inherit = barclass,
  -- lua
  number_dt = 0,
--  string_name = "morris",
--  boolean_crazy = true,
--  table_randomobject = {},
--  function_update = function(self,dt) self.dt = self.dt + dt end,
--  userdata_drawable = {},--love.graphics.newImage("butts.png"),  
--  thread_loader = coroutine.create(function() end),
  --[[
  -- nice?
  int_age = 12,
  readonly_int_starthp = 100,
  bag_children = nil,
  readonly_any_wat = nil,
  color_background = {255,255,255,255},
  -- love? (many other types missing!)
  image_spritesheet = love.graphics.newImage("map.png"),
  source_hit = love.audio.newSource("ouch.ogg"),
  --]]
}

foo = fooclass()

foo.dt = "potato"

print(foo.dt)