Test delegate with FFI struct.

fix_ffi_struct.patch

diff --git a/src/org/jruby/ext/ffi/Struct.java b/src/org/jruby/ext/ffi/Struct.java
index e6125f5..a851305 100644
--- a/src/org/jruby/ext/ffi/Struct.java
+++ b/src/org/jruby/ext/ffi/Struct.java
@@ -13,6 +13,7 @@ import org.jruby.exceptions.RaiseException;
 import org.jruby.runtime.ObjectAllocator;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
+import static org.jruby.runtime.Visibility.*;
 
 @JRubyClass(name="FFI::Struct", parent="Object")
 public class Struct extends RubyObject implements StructLayout.Storage {
@@ -115,7 +116,7 @@ public class Struct extends RubyObject implements StructLayout.Storage {
         return new Struct(runtime, (RubyClass) klass, getStructLayout(runtime, klass), ptr);
     }
 
-    @JRubyMethod(name = "initialize")
+    @JRubyMethod(name = "initialize", visibility = PRIVATE)
     public IRubyObject initialize(ThreadContext context) {
 
         memory = MemoryPointer.allocate(context.getRuntime(), layout.getSize(), 1, true);
@@ -123,7 +124,7 @@ public class Struct extends RubyObject implements StructLayout.Storage {
         return this;
     }
 
-    @JRubyMethod(name = "initialize")
+    @JRubyMethod(name = "initialize", visibility = PRIVATE)
     public IRubyObject initialize(ThreadContext context, IRubyObject ptr) {
         
         if (!(ptr instanceof AbstractMemory)) {
@@ -141,7 +142,7 @@ public class Struct extends RubyObject implements StructLayout.Storage {
         return this;
     }
 
-    @JRubyMethod(name = "initialize_copy")
+    @JRubyMethod(name = "initialize_copy", visibility = PRIVATE)
     public IRubyObject initialize_copy(ThreadContext context, IRubyObject other) {
         if (other == this) {
             return this;

rundelegate.rb

require 'ffi'
require 'delegate'

class A < FFI::Struct
    layout(
        :x, :int,
        :y, :int,
    )
end

class B < DelegateClass(A)
    def initialize
        @s = A.new
        super(@s)
    end
end

b = B.new
puts "B.new returns nil? #{b.nil?}"
b[:x] = 10
b[:y] = 20
puts "b[:x] = #{b[:x]}"
puts "b[:y] = #{b[:y]}"

Nicely done! I noticed the initialize thing too, but then in reproducing it I walked away from the culprit: Struct. I think you are exactly right, so file the bug with your patch and workaround and we will fix for 1.6.2.

Referencing the A.instance_methods.grep /init/ in MRI Ruby 1.9.2, you actually get this:
initialize_dup
initialize_clone
while JRuby gives this:
initialize
initialize_copy

Perhaps there is something need to be done to make these consistent :) Otherwise, any dynamic classes rely on these will break easily :p

The patch above doesn't remove the initialize_copy() from the list, may be I'll do that to make it consistent with MRI Ruby.