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➜ MUSHclient
➜ Lua
➜ Adding methods to an object
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Adding methods to an object
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| Posted by
| Blainer
(191 posts) Bio
|
| Date
| Sat 13 Jun 2009 02:19 AM (UTC) Amended on Sat 13 Jun 2009 03:04 AM (UTC) by Blainer
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| Message
| If I have:
assert (package.loadlib("sqlite3.dll","luaopen_luasql_sqlite3")) ()
aard_db = assert(sqlite3.open_memory("aard"))
And I want to add:
function aard_db:test(arg)
self.nrows(arg)
return something
end
So I can do this:
aard_db:test("something")
How do I do it? Can I create a class called aard_db and add the methods from sqlite3.dll?
| | Top |
|
| Posted by
| Nick Gammon
Australia (23,140 posts) Bio
Forum Administrator |
| Date
| Reply #1 on Sun 14 Jun 2009 09:17 PM (UTC) |
| Message
| It's not going to be too easy. The variable aard_db is a userdata, not a table, and thus you can't add more things to it. A userdata is just a 4-byte pointer to an internal structure used by the database routines.
The userdata aard_db already has a metatable as well, so you can't just add one. I experimented with something like this:
mt = getmetatable (aard_db)
mt.__index.test = function (arg)
print "in test"
return self.nrows (arg)
end -- function
This indeed lets you add "test" as a function for the metatable in aard_db, however it doesn't know the self variable. Maybe you can get something along those lines to work, I'm not sure. |
- Nick Gammon
www.gammon.com.au, www.mushclient.com | | Top |
|
| Posted by
| Erendir
Germany (47 posts) Bio
|
| Date
| Reply #2 on Sun 14 Jun 2009 11:27 PM (UTC) |
| Message
| just use this code:
mt.__index.test = function (self, arg)
print "in test"
return self.nrows (arg)
end -- function
or this:
function mt.__index:test(arg)
print "in test"
return self.nrows (arg)
end -- function
| | Top |
|
| Posted by
| Nick Gammon
Australia (23,140 posts) Bio
Forum Administrator |
| Date
| Reply #3 on Sun 14 Jun 2009 11:38 PM (UTC) Amended on Sun 14 Jun 2009 11:40 PM (UTC) by Nick Gammon
|
| Message
| That gave this error:
Run-time error
World: smaug
Immediate execution
[string "Immediate"]:9: bad argument #1 to 'nrows' (:sqlite3 expected, got string)
stack traceback:
[C]: in function 'nrows'
[string "Immediate"]:9: in function 'test'
[string "Immediate"]:13: in main chunk
However a slight modification seemed to work:
db=sqlite3.open(GetInfo (82)) -- open MUSHclient prefs file
mt = getmetatable (db)
mt.__index.test = function (self, arg)
print "in test"
return self:nrows (arg)
end -- function
require "tprint"
for row in db:test("SELECT * FROM sqlite_master") do
tprint (row)
end
db:close() -- close
|
- Nick Gammon
www.gammon.com.au, www.mushclient.com | | Top |
|
| Posted by
| Nick Gammon
Australia (23,140 posts) Bio
Forum Administrator |
| Date
| Reply #4 on Sun 14 Jun 2009 11:39 PM (UTC) |
| Message
|
Quote:
assert (package.loadlib("sqlite3.dll","luaopen_luasql_sqlite3")) ()
SQLite is built into MUSHclient these days, you don't need this line. |
- Nick Gammon
www.gammon.com.au, www.mushclient.com | | Top |
|
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