From 75b310a07894ce6e01e2f984850f40c7ef31b1cd Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Fri, 10 May 2019 11:23:19 +1000
Subject: [PATCH] Add convenience methods to `BeaconStateTypes`

---
 .../src/beacon_state/beacon_state_types.rs    | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/eth2/types/src/beacon_state/beacon_state_types.rs b/eth2/types/src/beacon_state/beacon_state_types.rs
index a3eedc8031..8f0f6d5245 100644
--- a/eth2/types/src/beacon_state/beacon_state_types.rs
+++ b/eth2/types/src/beacon_state/beacon_state_types.rs
@@ -13,9 +13,46 @@ pub trait BeaconStateTypes:
     type LatestSlashedExitLength: Unsigned + Clone + Sync + Send + Debug + PartialEq;
 
     fn spec() -> ChainSpec;
+
+    /// Returns the `SHARD_COUNT` constant for this specification.
+    ///
+    /// Spec v0.5.1
+    fn shard_count() -> usize {
+        Self::ShardCount::to_usize()
+    }
+
+    /// Returns the `SLOTS_PER_HISTORICAL_ROOT` constant for this specification.
+    ///
+    /// Spec v0.5.1
+    fn slots_per_historical_root() -> usize {
+        Self::SlotsPerHistoricalRoot::to_usize()
+    }
+
+    /// Returns the `LATEST_RANDAO_MIXES_LENGTH` constant for this specification.
+    ///
+    /// Spec v0.5.1
+    fn latest_randao_mixes_length() -> usize {
+        Self::LatestRandaoMixesLength::to_usize()
+    }
+
+    /// Returns the `LATEST_ACTIVE_INDEX_ROOTS` constant for this specification.
+    ///
+    /// Spec v0.5.1
+    fn latest_active_index_roots() -> usize {
+        Self::LatestActiveIndexRootsLength::to_usize()
+    }
+
+    /// Returns the `LATEST_SLASHED_EXIT_LENGTH` constant for this specification.
+    ///
+    /// Spec v0.5.1
+    fn latest_slashed_exit_length() -> usize {
+        Self::LatestSlashedExitLength::to_usize()
+    }
 }
 
 /// Ethereum Foundation specifications.
+///
+/// Spec v0.5.1
 #[derive(Clone, PartialEq, Debug, Default, Serialize, Deserialize)]
 pub struct FoundationStateTypes;
 
@@ -33,6 +70,9 @@ impl BeaconStateTypes for FoundationStateTypes {
 
 pub type FoundationBeaconState = BeaconState<FoundationStateTypes>;
 
+/// Ethereum Foundation specifications, modified to be suitable for < 1000 validators.
+///
+/// Spec v0.5.1
 #[derive(Clone, PartialEq, Debug, Default, Serialize, Deserialize)]
 pub struct FewValidatorsStateTypes;
 
@@ -50,6 +90,9 @@ impl BeaconStateTypes for FewValidatorsStateTypes {
 
 pub type FewValidatorsBeaconState = BeaconState<FewValidatorsStateTypes>;
 
+/// Specifications suitable for a small-scale (< 1000 validators) lighthouse testnet.
+///
+/// Spec v0.5.1
 #[derive(Clone, PartialEq, Debug, Default, Serialize, Deserialize)]
 pub struct LighthouseTestnetStateTypes;