Yes, thanks, I do know — but then you have to assume all cdata types have this
field, or it will fail at query (and you probably do not want to add a
metatable on simple cdata types).
Of course you can use a pcall(), but the JIT will bail out and return to
interpreter mode, in case of failure… which is not an option for me.
Ronan.
> On Nov 26, 2014, at 1:26 PM, Peter Colberg <peter@xxxxxxxxxxx> wrote:
>
> On Wed, Nov 26, 2014 at 11:51:07AM -0800, Ronan Collobert wrote:
>> More generally when one hides something in the metatable (a global
>> property of the “class” of a given object), right now one cannot
>> retrieve it easily. Once in while, the case occurs, someone
>> complains to me, and one has to play with the
>> tonumber(ffi.typeof())+additional table trick.
>
> Did you know this feature of ctypes?
>
> local ffi = require("ffi")
> local ctype = ffi.metatype("struct { int i; }", {
> __index = {
> class = "MyClass",
> size = function(self)
> return ffi.sizeof(self)
> end,
> }
> })
>
> assert(ctype.class == "MyClass")
> assert(ctype:size() == 4)
>
> local obj = ctype(123)
> local objtype = ffi.typeof(obj)
> assert(objtype.class == "MyClass")
> assert(objtype:size() == 4)
>
> That is the X to your Y :-).
>
> Peter
>
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