Hi. I’ve extended the class implementation provided by codea to support (even in a rough way) also interfaces implementation. I was looking for something similar to what AS3 allows to do, having no multiple inheritance but having single inheritance plus multiple interfaces implementation. The code is based on a ClassLib.lua I founded on lua-users.org.
-- Class.lua
-- Compatible with Lua 5.1 (not 5.0).
--[[
class(ancestor, interfaces...)
examples:
- class(base)
inherits from base, so is_a(base) is true
class(base, interface1,..,interfacen)
inheriths from base and implements all the interfaces, so
is_a is true only for base, while implements is true for all the interfaces, and also for base
class(nil, interface1,..,interfacen)
implements interfaces but without inheritance, so is_a is true only for self name and i plements is true for all the interfaces
---
pay attention to symbol redefinition. in init phase a warning is logged when a symbol is redefined but no more
--]]
local reserved =
{
__index = true,
_base = true,
is_a = true,
implements = true,
init = true
}
function class(...)
local c = {} -- a new class instance
local args = {...}
if table.getn(args) then
local base = args and args[1] or nil
if type(base) == 'table' then
-- our new class is a shallow copy of the base class!
for i,v in pairs(base) do
c[i] = v
end
c._base = base
end
table.remove(args,1)
for _,i in pairs(args) do
if type(i) =='table' then
for k,v in pairs(i) do
if not reserved[k] and type(i[k]) == 'function' then
if c[k] then
print("warning " .. k ..
" is already defined")
end
c[k] = v
end
end
end
end
end
-- the class will be the metatable for all its objects,
-- and they will look up their methods in it.
c.__index = c
-- expose a constructor which can be called by <classname>( <args> )
local mt = {}
mt.__call = function(class_tbl, ...)
local obj = {}
setmetatable(obj,c)
if class_tbl.init then
class_tbl.init(obj,...)
else
-- make sure that any stuff from the base class is
--initialized!
if base and base.init then
base.init(obj, ...)
end
end
return obj
end
c.is_a = function(self, klass)
local m = getmetatable(self)
while m do
if m == klass then return true end
m = m._base
end
return false
end
c.implements = function(self, interface)
-- Check we have all the target's callables
for k, v in pairs(interface) do
if not reserved[k] and type(v) == 'function' and
type(self[k]) ~= 'function' then
return false
end
end
return true
end
setmetatable(c, mt)
return c
end
