__len metamethod of pointer of struct
- From: Peter Colberg <peter@xxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Sat, 8 Sep 2012 14:16:47 -0400
Hi,
I would like to define a __len metamethod for an ffi struct type.
However, I do not have access to the struct itself, but to a pointer
to the struct:
local ffi = require("ffi")
ffi.cdef[[
typedef struct MPI_Info_t *MPI_Info;
int MPI_Info_get_nkeys(MPI_Info info, int *nkeys);
]]
The following test case reproduces the issue:
-- struct_ptr_len.lua
local ffi = require("ffi")
local ctype = ffi.typeof("struct { int len; }")
local ptype = ffi.typeof("$ *", ctype)
local function len(self) return self.len end
ffi.metatype(ctype, {__len = len, __tostring = len})
local val = ctype(42)
local ptr = ffi.cast(ptype, val)
assert(tostring(val) == 42)
assert(tostring(ptr) == 42)
assert(#val == 42)
assert(#ptr == 42)
The expression #ptr causes this error:
luajit: struct_ptr_len.lua:15: attempt to get length of 'struct 95 *'
stack traceback:
struct_ptr_len.lua:15: in main chunk
[C]: ?
Since __tostring works fine with a struct pointer, should __len work, too?
Thanks,
Peter
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