inheritance and sub-tables
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- Subject: inheritance and sub-tables
- From: arioch82 <arioch82@...>
- Date: 2014年2月26日 10:45:21 -0800 (PST)
Hi guys,
I have found some problems using inheritance in lua when my object contains
other tables and i was wondering if there's a better way to handle it.
The best way to explain it is through an example:
--------------------------------------------------------------
local luaprint = print
-- Class Template
local Class = {
New = function (self, obj)
local obj = obj or {}
setmetatable(obj, self)
self.__index = self
return obj
end
}
-- Base Class
local Base = Class:New {
name = "Base",
v1 = 1,
--------- OPTION 1 ---------
test = {
v2 = -1
},
--------- OPTION 1 ---------
print = function(self)
luaprint("name = " .. self.name .. ", v1 = " .. self.v1)
end
}
function Base.test.print()
luaprint("Class Base")
end
function Base.test.print_v(self)
luaprint("v2 = " .. self.v2)
end
-- First Class
local A = Base:New {
name = "A",
v1 = 2,
}
A.test.v2 = -2
function A.test.print()
luaprint("Class A")
end
-- Second Class
local B = Base:New {
name = "B",
v1 = 3,
}
B.test.v2 = -3
function B.test.print()
luaprint("Class B")
end
-- prints
Base:print()
Base.test.print()
Base.test:print_v()
A:print()
A.test.print()
A.test:print_v()
B:print()
B.test.print()
B.test:print_v()
--------------------------------------------------------------
Now the above code gives this output
--------- OUTPUT 1 ---------
name = Base, v1 = 1
Class B
v2 = -3
name = A, v1 = 2
Class B
v2 = -3
name = B, v1 = 3
Class B
v2 = -3
--------- OUTPUT 1 ---------
as you can see when B changes an element in the subtable "test" that value
will change for ALL instances.
A Fix for this is redefining the Base like this:
--------------------------------------------------------------
-- Base Class
local Base = Class:New {
name = "Base",
v1 = 1,
--------- OPTION 2 ---------
test = Class:New {
v2 = -1
},
New = function(self, obj)
local obj = Class.New(self, obj)
obj.test = self.test:New{}
return obj
end,
--------- OPTION 2 ---------
print = function(self)
luaprint("name = " .. self.name .. ", v = " .. self.v)
end
}
--------------------------------------------------------------
which then gives the expected output
--------- OUTPUT 2 ---------
name = Base, v1 = 1
Class Base
v2 = -1
name = A, v1 = 2
Class A
v2 = -2
name = B, v1 = 3
Class B
v2 = -3
--------- OUTPUT 2 ---------
I believe this happens because all tables are referenced whilst other types
are actually copied but i was wondering if there's any way to automate the
process / handle this in a better way as it's something that seems really
prone to errors that are hard to track down.
Thank you
--
View this message in context: http://lua.2524044.n2.nabble.com/inheritance-and-sub-tables-tp7656847.html
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