Change CTxDestination into a class to support serialization (WIP)

src/script.h

@@ -17,6 +17,7 @@
 #include "keystore.h"
 #include "prevector.h"
 #include <util/hash_type.h>
+#include "serialize.h"
 #include "wallet/ismine.h"
 
 typedef std::vector<unsigned char> valtype;
@@ -30,7 +31,14 @@ class CScriptID : public BaseHash<uint160>
     CScriptID() : BaseHash() {}
     explicit CScriptID(const CScript& in);
     explicit CScriptID(const uint160& in) : BaseHash(in) {}
-//    explicit CScriptID(const ScriptHash& in);
+
+    ADD_SERIALIZE_METHODS;
+
+    template <typename Stream, typename Operation>
+    inline void SerializationOp(Stream& s, Operation ser_action)
+    {
+        READWRITE(m_hash);
+    }
 };
 
 static const unsigned int MAX_SCRIPT_ELEMENT_SIZE = 520; // bytes
@@ -93,7 +101,66 @@ class CNoDestination {
  *  * CScriptID: TX_SCRIPTHASH destination
  *  A CTxDestination is the internal data type encoded in a CBitcoinAddress
  */
-typedef std::variant<CNoDestination, CKeyID, CScriptID> CTxDestination;
+typedef std::variant<CNoDestination, CKeyID, CScriptID> CTxDestinationVariant;
+
+class CTxDestination : public CTxDestinationVariant
+{
+public:
+    CTxDestination() : CTxDestinationVariant()
+    {}
+
+    CTxDestination(CTxDestination& dest) : CTxDestinationVariant(dest)
+    {}
+
+    CTxDestination(const CTxDestination& dest) : CTxDestinationVariant(dest)
+    {}
+
+    CTxDestination(CNoDestination dest) : CTxDestinationVariant(dest)
+    {}
+
+    CTxDestination(CKeyID dest) : CTxDestinationVariant(dest)
+    {}
+
+    CTxDestination(CScriptID dest) : CTxDestinationVariant(dest)
+    {}
+
+    ADD_SERIALIZE_METHODS;
+
+    template <typename Stream, typename Operation>
+    inline void SerializationOp(Stream& s, Operation ser_action)
+    {
+        // The implicit cast here is to reduce the size of the variant index for (de)serialization. We will never need more than
+        // 256 different types in CTxDestinationVariant.
+        uint8_t variant_idx = this->index();
+
+        READWRITE(variant_idx);
+
+        // There is no (de)serialization necessary for CNoDestination.
+        // The indexes are in order of the typedef variant types specified above in CTxDestinationVariant.
+        // If new destination types are added to CTxDestinationVariant, then the below will need to be
+        // extended.
+
+        if (variant_idx == 0) {
+            return;
+        }
+
+        if (variant_idx == 1) {
+            CKeyID dest = std::get<1>(*this);
+
+            READWRITE(dest);
+
+            this->emplace<1>(dest);
+        }
+
+        if (variant_idx == 2) {
+            CScriptID dest = std::get<2>(*this);
+
+            READWRITE(dest);
+
+            this->emplace<2>(dest);
+        }
+    }
+};
 
 const char* GetTxnOutputType(txnouttype t);