Mark Address and HashDigest as readonly #605

CHANGES.md

@@ -54,6 +54,7 @@ To be released.
  -  `Swarm<T>.PreloadAsync()` became to ignore peers with lower tip.  [[#592]]
  -  `KademliaProtocol<T>.RefreshTableAsync()` became to validate only stale
     peers.  [[#568], [#593]]
+ -  Marked `Address` and `HashDigest` as readonly.  [[#610]]
 
 ### Bug fixes
 
@@ -113,6 +114,8 @@ To be released.
 [#599]: https://github.com/planetarium/libplanet/pull/599
 [#602]: https://github.com/planetarium/libplanet/pull/602
 [#609]: https://github.com/planetarium/libplanet/pull/609
+[#610]: https://github.com/planetarium/libplanet/pull/610
+
 
 Version 0.6.0
 -------------

Libplanet/Address.cs

@@ -38,15 +38,17 @@ namespace Libplanet
     /// <seealso cref="PublicKey"/>
     [Serializable]
     [Equals]
-    public struct Address : ISerializable, IComparable<Address>, IComparable
+    public readonly struct Address : ISerializable, IComparable<Address>, IComparable
     {
         /// <summary>
         /// The <see cref="byte"/>s size that each <see cref="Address"/> takes.
         /// <para>It is 20 <see cref="byte"/>s.</para>
         /// </summary>
         public const int Size = 20;
 
-        private ImmutableArray<byte> _byteArray;
+        private static readonly byte[] _defaultByteArray = new byte[Size];
+
+        private readonly ImmutableArray<byte> _byteArray;
 
         /// <summary>
         /// Creates an <see cref="Address"/> instance from the given immutable <see
@@ -148,7 +150,7 @@ public ImmutableArray<byte> ByteArray
             {
                 if (_byteArray.IsDefault)
                 {
-                    _byteArray = new byte[Size].ToImmutableArray();
+                    return _defaultByteArray.ToImmutableArray();
                 }
 
                 return _byteArray;
@@ -166,7 +168,9 @@ public ImmutableArray<byte> ByteArray
         /// <seealso cref="ByteArray"/>
         /// <seealso cref="Address(byte[])"/>
         [Pure]
-        public byte[] ToByteArray() => ByteArray.ToArray();
+        public byte[] ToByteArray() => ByteArray.IsDefault
+            ? _defaultByteArray
+            : ByteArray.ToArray();
 
         /// <summary>
         /// Gets a mixed-case hexadecimal string of 40 letters that represent

Libplanet/HashDigest.cs

@@ -16,7 +16,7 @@ namespace Libplanet
     /// <typeparam name="T">A <see cref="HashAlgorithm"/> which corresponds to
     /// a digest.  This determines <see cref="Size"/> of a digest.</typeparam>
     /// <seealso cref="HashAlgorithm"/>
-    public struct HashDigest<T> : IEquatable<HashDigest<T>>
+    public readonly struct HashDigest<T> : IEquatable<HashDigest<T>>
         where T : HashAlgorithm
     {
         /// <summary>
@@ -29,13 +29,17 @@ public struct HashDigest<T> : IEquatable<HashDigest<T>>
         /// </summary>
         public static readonly int Size;
 
-        private ImmutableArray<byte> _byteArray;
+        private static readonly byte[] _defaultByteArray;
+
+        private readonly ImmutableArray<byte> _byteArray;
 
         static HashDigest()
         {
             var thunk = (T)typeof(T).GetMethod("Create", new Type[0]).Invoke(
                 null, new object[0]);
             Size = thunk.HashSize / 8;
+
+            _defaultByteArray = new byte[Size];
         }
 
         /// <summary>
@@ -85,7 +89,7 @@ public ImmutableArray<byte> ByteArray
             {
                 if (_byteArray.IsDefault)
                 {
-                    _byteArray = new byte[Size].ToImmutableArray();
+                    return _defaultByteArray.ToImmutableArray();
                 }
 
                 return _byteArray;
@@ -169,7 +173,9 @@ public bool Satisfies(long difficulty)
         /// </returns>
         /// <seealso cref="ByteArray"/>
         [Pure]
-        public byte[] ToByteArray() => ByteArray.ToArray();
+        public byte[] ToByteArray() => ByteArray.IsDefault
+            ? _defaultByteArray
+            : ByteArray.ToArray();
 
         /// <summary>
         /// Gets a hexadecimal representation of a digest.