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Re: Feature request: userdata slice

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> On Aug 19, 2015, at 11:49 PM, Dirk Laurie <dirk.laurie@gmail.com> wrote:
> 
> I think I understand it now, thanks to the messages of the past
> 16 hours. (In my timezone, people are just waking up.) The
> OP's use case has been clouding the issue. What is being
> proposed is much more versatile.
….
Good summary :) .. But I’m not sure I’m on board with the idea...
Since userdata is opaque to Lua, any operation on that userdata must involve a call to a C function with the userdata as an argument. Once you do this, all the issues discussed here go away; it’s easy to provide the extra metadata about a userdata using any number of indirection/tagging techniques at the C level, including lifetime management if you want to (for example) refcount etc.
However, any such technique is of course private to each developer. In addition, they will typically involve a more complex low-level C model (struct with pointers to structs etc). So the question is: Would there be a benefit in having an “official” way for Lua to perform this in a generic manner that everyone could leverage?
My opinion is NO, for the following reasons:
— Lua already has metatables and uservalues that can be attached to userdata. Why isn’t a conventional use of these facilities adequate?
— I think it would be difficult to come up with a design that was both sufficiently flexible and compact.
— As you have noted on many occasions, Roberto et al are very unlikely to consider such an addition unless there is a very strong case for it.
—Tim

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