cdata serialize with __eq metamethod

[sonoro1234]

Hi,

When doing bitser.dumps for a cdata (of type vec2) with __eq methamethod (via metatype) which expects two vec2 to compare I get an error in https://github.com/gvx/bitser/blob/master/bitser.lua#L231 because ffi.typeof(vec2) is not a vec2.

The purpose of https://github.com/gvx/bitser/blob/master/bitser.lua#L231 is to differentiate cdata from ctype and could be perhaps done other way: tostring(cdata_or_ctype):match"^ctype"

[gvx]

Could you provide a minimal code sample that reproduces the problem? That way I can test any potential solution.

I don't think the tostring approach will work, given the LuaJIT documentation:

s = tostring(cdata)

Returns a string representation of the value of 64 bit integers ("nnnLL" or "nnnULL") or complex numbers ("re±imi"). Otherwise returns a string representation of the C type of a ctype object ("ctype<type>") or a cdata object ("cdata<type>: address"), unless you override it with a __tostring metamethod (see ffi.metatype()).

[sonoro1234]

It is tostring(ctype) case. I will provide test case tomorrow.

[sonoro1234]

local ffi = require"ffi"
local bitser = require"bitser"

ffi.cdef [[
typedef struct vec2 { double x, y;       } vec2;
]]

local metav2 = {
    __eq = function(a,b) return a.x == b.x and a.y == b.y end,
    __tostring = function(v) return '<'..v.x..','..v.y..'>' end
}
metav2.__index = metav2
local vec2 = ffi.metatype('vec2',metav2)

local a = vec2(1,2)
local b = bitser.loads(bitser.dumps(a))

print(a,b)

It does error. Changing if ty == value then for if tostring(value):match"^ctype" then succeds

[gvx]

My issue with your proposed solution is that it will fail on ctypes with metatables like {__tostring = function(v) return 'ctype object' end}.

What seems to work fine is

local success, eq = pcall(function() return value == ty end)
if success and eq then

I'll add more test cases to the spec, but it seems to work, and the performance impact seems to be minimal.

[sonoro1234]

Yes, it works with provided example.