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➜ MUSHclient
➜ Lua
➜ Changes to the Lua initialization in MUSHclient v4.60
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Changes to the Lua initialization in MUSHclient v4.60
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| Posted by
| Nick Gammon
Australia (23,173 posts) Bio
Forum Administrator |
| Date
| Sun 05 Sep 2010 02:44 AM (UTC) Amended on Sun 05 Sep 2010 02:45 AM (UTC) by Nick Gammon
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| Message
| As part of code cleanups for version 4.60 of MUSHclient, I noticed that the implementation of the main script spaces metatables was wrong (it is confusing reading the C code to set it up).
To demonstrate, in any version below 4.60 you can try this:
print (_G) --> table: 00D0B6B8
print (world) --> table: 00CE6A38
print (rawget (_G, "__index")) --> nil
print (rawget (world, "__index")) --> table: 00CE6A38
print (getmetatable (_G)) --> table: 00CE6A38
print (getmetatable (world)) --> nil
world.__index = nil
Note "hello" --> Error: attempt to call global 'Note' (a nil value)
You can see that the above is wrong in a number of ways. It is as if this was coded in Lua:
setmetatable (_G, world)
world.__index = world
It should in fact look more like this:
setmetatable (_G, { __index = world } )
Also, setting world.__index to nil should not stop access to the world functions from the global environment.
In version 4.60 the results are like this:
print (_G) --> table: 020547A0
print (world) --> table: 0205ED30
print (rawget (_G, "__index")) --> nil
print (rawget (world, "__index")) --> nil
print (getmetatable (_G)) --> table: 0205EC90
print (getmetatable (world)) --> nil
world.__index = nil
Note "hello" --> hello
Now there is no "__index" field in the world table, and the global environment has a metatable which is different from the world table. This metatable simply indexes back to the world table. If you set world.__index it has no effect (it was nil anyway).
Now these changes *shouldn't* affect existing scripts, but I mention them in case anyone has done some obscure mucking around with metatables and are relying on the current behaviour. |
- Nick Gammon
www.gammon.com.au, www.mushclient.com | | Top |
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| Posted by
| Twisol
USA (2,257 posts) Bio
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| Date
| Reply #1 on Sun 05 Sep 2010 03:02 AM (UTC) |
| Message
| Fun side effect of the pre-4.60 behavior: you can access the world table as __index, too.
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'Soludra' on Achaea
Blog: http://jonathan.com/
GitHub: http://github.com/Twisol | | Top |
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| Posted by
| Nick Gammon
Australia (23,173 posts) Bio
Forum Administrator |
| Date
| Reply #2 on Sun 05 Sep 2010 03:16 AM (UTC) |
| Message
| Yeah, exactly why it was wrong. ;)
Well spotted. |
- Nick Gammon
www.gammon.com.au, www.mushclient.com | | Top |
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