Re: Different behavior when __index is a table or a function
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- Subject: Re: Different behavior when __index is a table or a function
- From: Procházka Lukáš Ing. - Pontex s. r. o. <LPr@...>
- Date: 2014年10月23日 10:41:58 +0200
Hello,
-- as I also need to solve this --
another (simplified) example:
----
local mt =
{ __index =
{ --a = "aaa",
},
--function(t, k) print("mt", t, k) end
}
local mt2 =
{ __index =
--{ a = "AAA",
--},
function(ttt, k) print("mt2", ttt, k) end -- [1]
}
setmetatable(mt.__index, mt2)
local t = setmetatable({}, mt)
print(t, mt, mt.__index, mt2, mt2.__index, t.a)
----
yields:
----
C:\Lukas>Test.lua
mt2 table: 003CB108 a
table: 003CB4A0 table: 003CAD50 table: 003CB108 table: 003CB430 function: 003CB480 nil
----
Function [1] receives 'mt2.__index' as 'ttt' argument ('table: 003CB108'), which is in agreement with Lua manual but is a bit useless when we are operating with table 't' (or - in another case it may be userdata).
So, question: how to (anyhow) pass the table 't' to the function [1] so that be able to access 't' members?
Which skill/trick/algorithm to use here?
Best regards,
Lukas
On 2014年10月22日 01:54:28 +0200, Philipp Janda <siffiejoe@gmx.net> wrote:
Am 21.10.2014 um 19:11 schröbte Andre Arpin:
This post is long so I remove all quotes
Note: the unexpected value of self when o.baz is invoked.
This is exactly the same problem as before: `o:baz()` involves two
distinct operations: one `__index` call to retrieve the `baz` function,
and finally one call to that `baz` function. The `__index` function and
the `baz` function may (and in this case will) be called with different
`self` arguments. You are trying to do all the work in the `__index`
function alone:
setmetatable(getmetatable(metainstance.__index).__index, {
__index = function(self, key)
This `self` is always the same as
`getmetatable(metainstance.__index).__index`, *not* `o`.
print(self, key, "self, key")
dump(self, 'self')
for k,v in pairs(self) do
print(k, v, 'k,v')
end
if key == "baz" then
print(type(self), (self).v)
return rawget(self,'v')
Here you are trying to access `o` (the object before the colon operator
in `o:baz()`), but it is simply not available here. You have to return a
function reference at this point, which in turn will be called with the
`self` value you expect (i.e. `o`).
end
end,
})
Philipp
--
Ing. Lukáš Procházka | mailto:LPr@pontex.cz
Pontex s. r. o. | mailto:pontex@pontex.cz | http://www.pontex.cz
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