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- Subject: Re: Possible improvements to the LNUM patch?
- From: Ralph Hempel <rhempel@...>
- Date: Tue, 15 Apr 2008 08:21:35 -0400
Dirk Feytons wrote:
On Mon, Apr 14, 2008 at 9:53 PM, Ralph Hempel
I would suggest having a look at creating your own userata for
high precision monetary values, and implementing a metatable
with overrides for the basic Lua operations.
You may also end up having to add functions to create instances
of the type etc. See the C API and userdata secions in the Blue PiL
I recently discovered one disadvantage of such an approach: relational
operators are only possible on operands of the same type. In other
words, you can't compare such a userdata object with a regular number
since it is by definition false. This might or might not be a problem,
depending on your specific needs but it's certainly something to keep
These can be implemented in the metatable as well. The Lua VM
determines that one side or the other of the comparison is a
userdata and then calls the operator in the metatable for that
It is up to the C implementation of the userdata to either
issue an error message or make an attempt to cast the other
side of the operator if necessary.
It's probably best in this application to have a completely
separate userdata that is incompatible with "regular" Lua numbers.
At least you'll get decent error messages if you do mix up
the operands :-)