Idea (unsafe): a variant of lua_getstack
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- Subject: Idea (unsafe): a variant of lua_getstack
- From: Eduardo Ochs <eduardoochs@...>
- Date: 2012年2月21日 07:23:15 -0200
Two questions - one technical, one not...
1) Is there a way to flag clearly to the list that a certain idea is
for a low-level/dangerous hack ONLY, and only meant as a prototype
and for quick experiments that would be run only a handful of times
and in very controlled environments? I would like to avoid getting
answers like "don't do that, it's unsafe", "how would you handle
GC?", "use userdata", "this won't work in architectures where
pointers can not be represented faithfully as numbers"... Sometimes
in a proof of concept it is better to leave all concerns with GC,
safety, etc to a second moment...
2) I would like to experiment with variants of lua_getstack,
debug.getinfo, debug.getlocal and debug.setlocal - see:
http://www.lua.org/source/5.2/ldblib.c.html#dblib
http://www.lua.org/source/5.2/ldblib.c.html#db_getinfo
http://www.lua.org/source/5.2/ldblib.c.html#db_getlocal
http://www.lua.org/source/5.2/ldblib.c.html#db_setlocal
http://www.lua.org/source/5.2/ldebug.c.html#lua_getstack
http://www.lua.org/manual/5.2/manual.html#lua_getstack
http://www.lua.org/manual/5.2/manual.html#lua_getinfo
http://www.lua.org/manual/5.2/manual.html#lua_getlocal
http://www.lua.org/manual/5.2/manual.html#lua_setlocal
http://www.lua.org/manual/5.2/manual.html#pdf-debug.getinfo
http://www.lua.org/manual/5.2/manual.html#pdf-debug.getlocal
http://www.lua.org/manual/5.2/manual.html#pdf-debug.setlocal
in which the "level" parameter could also be given as a string of
the form "0xhhhhhhhh", meaning the address in memory - without any
kind of error checking - of an active function. Is there something
like this around? I haven't started to write the code for this yet,
and my C skills got quite rusty in the last years, so I'd rather
start with someone else's code...
If it is not clear how these variants could be useful, consider
this:
inner = function ()
print(debug.getlocal(2, 1)) --> a 22
print(debug.setlocal(2, 1, 33)) --> a
end
outer = function ()
local a = 22
print(a) --> 22
inner()
print(a) --> 33
end
outer()
and this pseudocode, where _L is a table that gives access to the
local variables of the function "outer":
inner = function (_L)
print(_L.a) --> 22
_L.a = 33
end
outer = function ()
local a = 22
_L = setmetable({}, {__index = ..., __newindex = ...})
print(a) --> 22
inner(_L)
print(a) --> 33
end
outer()
It is possible to write the code for "_L" in standard Lua using the
debug library, but that requires a lot of juggling with the stack
depth.
Cheers,
Eduardo Ochs
eduardoochs@gmail.com
http://angg.twu.net/