Re: Lua 5.0 (alpha) comments

[Roberto Ierusalimschy <roberto@...>]

> There is a mistake in the manual on page 22.

Yes, thanks.


> There are still a few undocumented features like __tostring, __metatable,
> and table.concat which should be advertised more.

Unfortunately, there are many undocumented features yet :-(


> I find newproxy a curious addition.  It gives you unique userdata that
> share the same metatable.  I cannot think of a use for it yet.
> What did you have in mind?

This is a very experimental feature. We wanted a simple and secure way
of creating userdata in Lua. It has several uses, such as to monitor
garbage collection, as a light "unique" object, and for testing ;-).
But we cannot allow Lua to change the metatable of those userdata;
otherwise, Lua could break other libraries (e.g. give one of these
userdata as a file to be closed). To allow each userdata to have its own
new metatable or to share the metatable of another such userdata seems
flexible and secure.


> I like pairs and ipairs, (especially now that table.getn(t) is extra
> verbose), but ipairs can fool you if you put nil in the middle of your
> table.

Note that the new "table.getn" will also fool you in this case. If
you really need nils in the array (instead of false), you must use
table.setn and then table.getn.

-- Roberto