Re: type checking tags
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- Subject: Re: type checking tags
- From: Reuben Thomas <rrt@...>
- Date: 2002年1月24日 09:45:23 +0000 (GMT)
> -- this will hang
> p = 123
> s = read(p,'*a')
That is bad. The type of file handle arguments should be checked.
> -- this will give error
> q = 'I love you'
> t = read(q,'*a')
This is no problem: Lua 4.0 is assuming you're trying to use a Lua 3.2
read pattern
> So mytag becomes global and next time I can check if the
> pointer passed is a valid myuserdata. But wait a minute.
> Someone can erase mytag or set it to something else. So
> what really is the philosophy behind tag?
You should implement tags for userdata in a different way, e.g. the way
that the I/O library does: in particular, store the value in a C variable,
which can't be overwritten, not a Lua variable.
--
http://sc3d.org/rrt/ | Slow Pedestrian Crossing