Re: A way to associate a Lua value with a FFI pointer?
- From: Daniel Kolesa <quaker66@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Wed, 9 Apr 2014 10:51:17 +0100
Yes, I know this. But that's not relevant in my case and the cases you're
showing do not happen in my particular situation :)
2014-04-09 10:47 GMT+01:00 Richard Hundt <richardhundt@xxxxxxxxx>:
> On 4/9/14 11:31 AM, Daniel Kolesa wrote:
> > The address in C stays constant, so there should be no problem with
> > using cdata as a key here.
>
> That the address in C stays constant doesn't mean much. That's my point.
>
> ```C
> int is_equal(char* a, char* b) {
> return a == b;
> }
> ```
>
> ```Lua
> a = ffi.new('char[1]')
> b = ffi.cast('char*', a)
>
> assert(ffi.C.is_equal(a, b) == 1)
>
> assert(a == b) -- even this works (git head)
> t = { }
> t[a] = 42
> assert(t[b] == nil) -- yep
> ```
>
> That C function cannot tell the difference between `a` and `b` because
> the addresses are the same. However, even so, you can't use `b` as a key
> where previously you used `a`.
>
> Maybe you already know all this, and I'm just making a noise, but
> perhaps somebody else who's reading this can benefit. It crops up
> occasionally.
>
>
>
>
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