inheritance.lua

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-- Yet Another Class Implementation (version 1.2)
--
-- Julien Patte [julien.patte AT gmail DOT com] - 25 Feb 2007
--
-- Inspired from code written by Kevin Baca, Sam Lie, Christian Lindig and others
-- Thanks to Damian Stewart and Frederic Thomas for their interest and comments
-----------------------------------------------------------------------------------

do  -- keep local things inside

-- associations between an object an its meta-informations
-- e.g its class, its "lower" object (if any), ...
local metaObj = {}
setmetatable(metaObj, {__mode = "k"})

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-- internal function 'duplicate'
-- return a shallow copy of table t

local function duplicate(t)
  local t2 = {}
  for k,v in pairs(t) do t2[k] = v end
  return t2
end
  
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-- internal function 'newInstance'

local function newInstance(class, ...) 

  local function makeInstance(class, virtuals)
    local inst = duplicate(virtuals)
    metaObj[inst] = { obj = inst, class = class }
  
    if class:super()~=nil then
      inst.super = makeInstance(class:super(), virtuals)
      metaObj[inst].super = metaObj[inst.super] -- meta-info about inst
      metaObj[inst.super].lower = metaObj[inst]
    else 
      inst.super = {}
    end 
  
    setmetatable(inst, class.static)
  
    return inst
  end
 
  local inst = makeInstance(class, metaObj[class].virtuals) 
  inst:init(...)
  return inst
end

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-- internal function 'makeVirtual'

local function makeVirtual(class, fname) 
  local func = class.static[fname]
  if func == nil then 
    func = function() error("Attempt to call an undefined abstract method '"..fname.."'") end
   end
  metaObj[class].virtuals[fname] = func
end

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-- internal function 'trycast'
-- try to cast an instance into an instance of one of its super- or subclasses

local function tryCast(class, inst) 
  local meta = metaObj[inst]
  if meta.class==class then return inst end -- is it already the right class?
  
  while meta~=nil do  -- search lower in the hierarchy
    if meta.class==class then return meta.obj end
    meta = meta.lower
  end
  
  meta = metaObj[inst].super  -- not found, search through the superclasses
  while meta~=nil do  
    if meta.class==class then return meta.obj end
    meta = meta.super
  end
  
  return nil -- could not execute casting
end

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-- internal function 'secureCast'
-- same as trycast but raise an error in case of failure

local function secureCast(class, inst) 
  local casted = tryCast(class, inst)
  if casted == nil then 
  error("Failed to cast " .. tostring(inst) .. " to a " .. class:name())
  end
  return casted
end

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-- internal function 'classMade'

local function classMade(class, obj) 
  if metaObj[obj]==nil then return false end -- is this really an object?
  return (tryCast(class,obj) ~= nil) -- check if that class could cast the object
end


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-- internal function 'callup'
-- Function used to transfer a method call from a class to its superclass

local callup_inst
local callup_target

local function callup(inst, ...)
  return callup_target(callup_inst, ...)  -- call the superclass' method
end


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-- internal function 'subclass'

local function inst_init_def(inst,...) 
  inst.super:init() 
end

local function inst_newindex(inst,key,value)              
  if inst.super[key] ~= nil then  -- First check if this field isn't already
                  -- defined higher in the hierarchy
  inst.super[key] = value;    -- Update the old value
  else 
    rawset(inst,key,value);     -- Create the field
  end
end

local function subclass(baseClass, name) 
  if type(name)~="string" then name = "Unnamed" end
  --outputChatBox(name)
  local theClass = {}

  -- need to copy everything here because events can't be found through metatables
  local b = baseClass.static
  local inst_stuff = { __tostring=b.__tostring, __eq=b.__eq, __add=b.__add, __sub=b.__sub, 
  __mul=b.__mul, __div=b.__div, __mod=b.__mod, __pow=b.__pow, __unm=b.__unm, 
  __len=b.__len, __lt=b.__lt, __le=b.__le, __concat=b.__concat, __call=b.__call}
 
  inst_stuff.init = inst_init_def
  inst_stuff.__newindex = inst_newindex
  function inst_stuff.class() return theClass end

  function inst_stuff.__index(inst, key) -- Look for field 'key' in instance 'inst'
  local res = inst_stuff[key]     -- Is it present?
  if res~=nil then return res end   -- Okay, return it
  
  res = inst.super[key]         -- Is it somewhere higher in the hierarchy?
  
  if type(res)=='function' and
    res ~= callup then        -- If it is a method of the superclass,
    callup_inst = inst.super      -- we will need to do a special forwarding
    callup_target = res       -- to call 'res' with the correct 'self'
    return callup           -- The 'callup' function will do that
  end
  
  return res
  end
 

  local class_stuff = { static = inst_stuff, made = classMade, new = newInstance,
  subclass = subclass, virtual = makeVirtual, cast = secureCast, trycast = tryCast }
  metaObj[theClass] = { virtuals = duplicate(metaObj[baseClass].virtuals) }
  
  function class_stuff.name(class) return name end
  function class_stuff.super(class) return baseClass end
  function class_stuff.inherits(class, other) 
  return (baseClass==other or baseClass:inherits(other)) 
  end
 
  local function newmethod(class, name, meth)
  inst_stuff[name] = meth;
  if metaObj[class].virtuals[name]~=nil then 
    metaObj[class].virtuals[name] = meth  
  end
  end
  
  local function tos() return ("class "..name) end
  setmetatable(theClass, { __newindex = newmethod, __index = class_stuff, 
  __tostring = tos, __call = newInstance } )
 
  return theClass
end

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-- The 'Object' class
---@type Object
Object = {}

local function obj_newitem() error "May not modify the class 'Object'. Subclass it instead." end
local obj_inst_stuff = {}
function obj_inst_stuff.init(inst,...) end
obj_inst_stuff.__index = obj_inst_stuff
obj_inst_stuff.__newindex = obj_newitem
function obj_inst_stuff.class() return Object end
function obj_inst_stuff.__tostring(inst) return ("a "..inst:class():name()) end

local obj_class_stuff = { static = obj_inst_stuff, made = classMade, new = newInstance,
  subclass = subclass, cast = secureCast, trycast = tryCast }
function obj_class_stuff.name(class) return "Object" end
function obj_class_stuff.super(class) return nil end
function obj_class_stuff.inherits(class, other) return false end
metaObj[Object] = { virtuals={} }

local function tos() return ("class Object") end
setmetatable(Object, { __newindex = obj_newitem, __index = obj_class_stuff, 
  __tostring = tos, __call = newInstance } )

----------------------------------------------------------------------
-- function 'newclass'
---@return #Object description
function newclass(name, baseClass)
 baseClass = baseClass or Object
 return baseClass:subclass(name)
end

end -- 2 global things remain: 'Object' and 'newclass'

-- end of code