[SOLVED] How to copy an instance of the Ruby Fiddle struct?

How to copy an instance of the Ruby Fiddle struct?

It's not obvious how to copy an instance of the Fiddle struct. I found an ugly solution using the Fiddle::Pointer like this.

require 'fiddle/import'

X = Fiddle::Importer.struct [
  'int a',
  'int b',
]

x = X.malloc
x.a = 1
x.b = 2

x2 = X.malloc
Fiddle::Pointer.new(x2.to_i)[0, X.size] = x.to_ptr.to_s
x2.b = 3
p [x.b, x2.b]

Is there a better way of doing this? One other way I thought of was using the []= operator of the super class(Fiddle::Pointer) of the x2.to_ptr, but it was worse than the above solution.

Solution

The class returned by Fiddle::Importer.struct implements [] and []= to retrieve and set the struct members by name:

x['a'] #=> 1
x['b'] #=> 2

However, when called with 2 arguments, these methods behave like their Fiddle::Pointer counterparts and get / set the raw binary data:

x[0, 4] #=> "\x01\x00\x00\x00"   <- a's binary data
x[4, 4] #=> "\x02\x00\x00\x00"   <- b's binary data

x[4, 4] = [-5].pack('l') #=> "\xFB\xFF\xFF\xFF"
x.b #=> -5

To copy x's entire data to x2:

x2[0, X.size] = x[0, X.size]

x2.a #=> 1
x2.b #=> 2