Re: assigning FFI metatype & gc to typedef'd struct ptr
- From: GrrrWaaa <grrrwaaa@xxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Mon, 14 May 2012 10:48:37 -0700
On May 14, 2012, at 2:33 AM, Mike Pall wrote:
> GrrrWaaa wrote:
>> According to [1] a metatype cannot be attached to a pointer
>> type, but instead to the underlying object. This doesn't work
>> out-of-the-box for opaque struct pointers, unless the struct is
>> also typedef'd:
>
> This is not true.
Ah - I misunderstood "Metatypes are always bound to the underlying aggregate
and not to any pointer type." as prescriptive rather than descriptive.
>
>> ffi.cdef[[
>> typedef struct OpaqueObject OpaqueObject; // won't work without
>> this line
>> typedef struct OpaqueObject * ObjectPtr;
>> ]]
>>
>> local mt = {}
>> -- <configure mt here>
>> ffi.metatype(ffi.typeof("OpaqueObject"), mt)
>
> Of course the first declaration is needed here because you are
> referring to "OpaqueObject", which isn't defined without this.
> We're talking about C declarations, not C++.
Ok. The C header I'm parsing never declared "struct OpaqueObject", so I had to
manually add it; but its definitely nicer they way you suggest:
> Or simply use
> "struct OpaqueObject" which works without the first declaration,
> because it's implicitly declared by the second declaration.
>
> Also, you can strip that ffi.typeof(). ffi.metatype() directly
> accepts an abstract type declaration (and returns a ctype object):
>
> local ootype = ffi.metatype("struct OpaqueObject", mt)
A lot cleaner, thanks!
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