Rename BeaconState fork_data to fork

And rename `ForkData` class to `Fork`.
Brings code into line with 0.1 spec, and addresses part of Consensys#235.

ethereum/datastructures/src/main/java/tech/pegasys/artemis/datastructures/state/ForkData.java → ethereum/datastructures/src/main/java/tech/pegasys/artemis/datastructures/state/Fork.java

@@ -15,13 +15,13 @@
 
 import com.google.common.primitives.UnsignedLong;
 
-public class ForkData {
+public class Fork {
 
   private UnsignedLong pre_fork_version;
   private UnsignedLong post_fork_version;
   private UnsignedLong fork_slot;
 
-  public ForkData(
+  public Fork(
       UnsignedLong pre_fork_version, UnsignedLong post_fork_version, UnsignedLong fork_slot) {
     this.pre_fork_version = pre_fork_version;
     this.post_fork_version = post_fork_version;

ethereum/statetransition/src/main/java/tech/pegasys/artemis/statetransition/BeaconState.java

@@ -51,7 +51,7 @@
 import tech.pegasys.artemis.datastructures.operations.DepositInput;
 import tech.pegasys.artemis.datastructures.state.CandidatePoWReceiptRootRecord;
 import tech.pegasys.artemis.datastructures.state.CrosslinkRecord;
-import tech.pegasys.artemis.datastructures.state.ForkData;
+import tech.pegasys.artemis.datastructures.state.Fork;
 import tech.pegasys.artemis.datastructures.state.PendingAttestationRecord;
 import tech.pegasys.artemis.datastructures.state.ShardCommittee;
 import tech.pegasys.artemis.datastructures.state.ShardReassignmentRecord;
@@ -67,7 +67,7 @@ public class BeaconState {
   // Misc
   private long slot;
   private long genesis_time;
-  private ForkData fork_data;
+  private Fork fork;
 
   // Validator registry
   private Validators validator_registry;
@@ -119,7 +119,7 @@ public BeaconState(
       // Misc
       long slot,
       long genesis_time,
-      ForkData fork_data,
+      Fork fork,
       // Validator registry
       Validators validator_registry,
       ArrayList<Double> validator_balances,
@@ -150,7 +150,7 @@ public BeaconState(
     // Misc
     this.slot = slot;
     this.genesis_time = genesis_time;
-    this.fork_data = fork_data;
+    this.fork = fork;
 
     // Validator registry
     this.validator_registry = validator_registry;
@@ -205,7 +205,7 @@ public BeaconState get_initial_beacon_state(
             // Misc
             INITIAL_SLOT_NUMBER,
             genesis_time,
-            new ForkData(
+            new Fork(
                 UnsignedLong.valueOf(INITIAL_FORK_VERSION),
                 UnsignedLong.valueOf(INITIAL_FORK_VERSION),
                 UnsignedLong.valueOf(INITIAL_SLOT_NUMBER)),
@@ -350,8 +350,7 @@ private boolean validate_proof_of_possession(
             Bytes48.leftPad(proof_of_possession.get(0)),
             Bytes48.leftPad(proof_of_possession.get(1)));
     UnsignedLong domain =
-        UnsignedLong.valueOf(
-            get_domain(state.fork_data, toIntExact(state.getSlot()), DOMAIN_DEPOSIT));
+        UnsignedLong.valueOf(get_domain(state.fork, toIntExact(state.getSlot()), DOMAIN_DEPOSIT));
     return bls_verify(
         pubkey, TreeHashUtil.hash_tree_root(proof_of_possession_data.toBytes()), signature, domain);
   }
@@ -443,25 +442,25 @@ private int indexOfPubkey(Bytes48[] validator_pubkeys, Bytes48 pubkey) {
   }
 
   /**
-   * @param fork_data
+   * @param fork
    * @param slot
    * @param domain_type
    * @return
    */
-  private int get_domain(ForkData fork_data, int slot, UnsignedLong domain_type) {
-    return get_fork_version(fork_data, slot) * (int) Math.pow(2, 32) + domain_type.intValue();
+  private int get_domain(Fork fork, int slot, UnsignedLong domain_type) {
+    return get_fork_version(fork, slot) * (int) Math.pow(2, 32) + domain_type.intValue();
   }
 
   /**
-   * @param fork_data
+   * @param fork
    * @param slot
    * @return
    */
-  private int get_fork_version(ForkData fork_data, int slot) {
-    if (slot < fork_data.getFork_slot().longValue()) {
-      return toIntExact(fork_data.getPre_fork_version().longValue());
+  private int get_fork_version(Fork fork, int slot) {
+    if (slot < fork.getFork_slot().longValue()) {
+      return toIntExact(fork.getPre_fork_version().longValue());
     } else {
-      return toIntExact(fork_data.getPost_fork_version().longValue());
+      return toIntExact(fork.getPost_fork_version().longValue());
     }
   }
 
@@ -839,12 +838,12 @@ public void setGenesis_time(long genesis_time) {
     this.genesis_time = genesis_time;
   }
 
-  public ForkData getFork_data() {
-    return fork_data;
+  public Fork getFork() {
+    return fork;
   }
 
-  public void setFork_data(ForkData fork_data) {
-    this.fork_data = fork_data;
+  public void setFork(Fork fork) {
+    this.fork = fork;
   }
 
   public Validators getValidator_registry() {

ethereum/statetransition/src/test/java/tech/pegasys/artemis/statetransition/BeaconStateTest.java

@@ -41,7 +41,7 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import tech.pegasys.artemis.datastructures.operations.AttestationData;
-import tech.pegasys.artemis.datastructures.state.ForkData;
+import tech.pegasys.artemis.datastructures.state.Fork;
 import tech.pegasys.artemis.datastructures.state.ShardCommittee;
 import tech.pegasys.artemis.datastructures.state.ValidatorRecord;
 import tech.pegasys.artemis.datastructures.state.Validators;
@@ -55,7 +55,7 @@ private BeaconState newState() {
         new BeaconState(
             0,
             0,
-            new ForkData(UnsignedLong.ZERO, UnsignedLong.ZERO, UnsignedLong.ZERO),
+            new Fork(UnsignedLong.ZERO, UnsignedLong.ZERO, UnsignedLong.ZERO),
             new Validators(),
             new ArrayList<>(),
             0,
@@ -446,9 +446,9 @@ void deepCopyBeaconState() {
     assertThat(deepCopy.getSlot()).isNotEqualTo(state.getSlot());
 
     // Test fork_data
-    state.setFork_data(new ForkData(UnsignedLong.valueOf(1), UnsignedLong.ONE, UnsignedLong.ONE));
-    assertThat(deepCopy.getFork_data().getPre_fork_version())
-        .isNotEqualTo(state.getFork_data().getPre_fork_version());
+    state.setFork(new Fork(UnsignedLong.valueOf(1), UnsignedLong.ONE, UnsignedLong.ONE));
+    assertThat(deepCopy.getFork().getPre_fork_version())
+        .isNotEqualTo(state.getFork().getPre_fork_version());
 
     // Test validator registry
     ArrayList<ValidatorRecord> new_records =