Mark BFSparse lazy val BFInstance as @transient

algebird-core/src/main/scala/com/twitter/algebird/BloomFilter.scala

@@ -156,7 +156,7 @@ case class BFSparse(hashes : BFHash, bits : CBitSet, width : Int) extends BF {
 
   lazy val numHashes: Int = hashes.size
 
-  lazy val dense : BFInstance = BFInstance(hashes, bits.toBitSet(width), width)
+  @transient lazy val dense : BFInstance = BFInstance(hashes, bits.toBitSet(width), width)
 
   def ++ (other: BF): BF = {
     require(this.width == other.width)

algebird-test/src/test/scala/com/twitter/algebird/BloomFilterTest.scala

@@ -6,6 +6,7 @@ import org.scalacheck.Arbitrary
 import org.scalacheck.Arbitrary.arbitrary
 import org.scalacheck.Properties
 import org.scalacheck.Gen.choose
+import java.io.{ObjectOutputStream, ByteArrayOutputStream}
 
 object BloomFilterLaws extends Properties("BloomFilter") {
   import BaseProperties._
@@ -99,5 +100,24 @@ class BloomFilterTest extends Specification {
         }
       }
     }
+
+    "not serialize BFInstance" in {
+      def serialize(bf: BF) = {
+        val stream = new ByteArrayOutputStream()
+        val out = new ObjectOutputStream(stream)
+        out.writeObject(bf)
+        out.close()
+        stream.close()
+        stream.toByteArray
+      }
+
+      val items = (1 until 10).map { _.toString }
+      val bf = BloomFilter(10, 0.1, SEED).create(items: _*)
+      val bytesBeforeSizeCalled = new String(serialize(bf))
+      bf.size
+      bf.contains("1").isTrue must be_==(true)
+      val bytesAfterSizeCalled = new String(serialize(bf))
+      bytesBeforeSizeCalled mustEqual bytesAfterSizeCalled
+    }
   }
 }