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Dirk Feytons wrote:
On Mon, Apr 14, 2008 at 9:53 PM, Ralph Hempel <rhempel@hempeldesigngroup.com> wrote:
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 for details.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 in mind.
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 userdata. 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 :-) Ralph