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: Philipp Janda <siffiejoe@...>
- Date: 2014年10月21日 12:13:16 +0200
Am 21.10.2014 um 10:07 schröbte Paco Zamora Martínez:
You make the point:
"the arguments of the `__index` call might not be the top level object
depending on how deep the chain is"
Which rules define the top level object?
With "top level object" I meant the thing in front of the colon operator
(the `o` in `o:foo()`), which is also the first table that has its
`__index` triggered. It is not an official term.
In the example send by Daurnimator, the __index in the first level is
receiving the caller object. So, in case of a second level of indirection,
it will receive the previous level metatable? So, given whatever a object,
its metatable b, and metatable of metatable c, the __index of b will
receive a, and the __index of c will receive b as argument.
No. If `a_meta` is the metatable of table `a` and contains an `__index`
function, that `__index` function will always receive table `a` as first
parameter even if that `__index` function is triggered at the end of an
`__index` chain. See for yourself:
local function foo_method( self )
print( "method foo called with self:", self )
end
local a = {}
local a_meta = {
__index = function( t, k )
print( "a_meta.__index function called with:", t )
return foo_method
end,
__tostring = function() return "a" end,
}
setmetatable( a, a_meta )
local b = {}
local b_meta = {
__index = a,
__tostring = function() return "b" end,
}
setmetatable( b, b_meta )
local c = {}
local c_meta = {
__index = b,
__tostring = function() return "c" end,
}
setmetatable( c, c_meta )
local d = {}
local d_meta = {
__index = c,
__tostring = function() return "d" end,
}
setmetatable( d, d_meta )
a:foo()
b:foo()
c:foo()
d:foo()
Philipp