Templatize ValidationState instead of subclassing

This removes boilerplate code in the subclasses which otherwise only
differ by the result type.

Author: jkczyz

src/consensus/validation.h

@@ -16,7 +16,7 @@
   * provider of the transaction should be banned/ignored/disconnected/etc.
   */
 enum class TxValidationResult {
-    TX_RESULT_UNSET,         //!< initial value. Tx has not yet been rejected
+    TX_RESULT_UNSET = 0,     //!< initial value. Tx has not yet been rejected
     TX_CONSENSUS,            //!< invalid by consensus rules
     /**
      * Invalid by a change to consensus rules more recent than SegWit.
@@ -50,7 +50,7 @@ enum class TxValidationResult {
   * useful for some other use-cases.
   */
 enum class BlockValidationResult {
-    BLOCK_RESULT_UNSET,      //!< initial value. Block has not yet been rejected
+    BLOCK_RESULT_UNSET = 0,  //!< initial value. Block has not yet been rejected
     BLOCK_CONSENSUS,         //!< invalid by consensus rules (excluding any below reasons)
     /**
      * Invalid by a change to consensus rules more recent than SegWit.
@@ -71,30 +71,31 @@ enum class BlockValidationResult {
 
 
 
-/** Base class for capturing information about block/transaction validation. This is subclassed
+/** Template for capturing information about block/transaction validation. This is instantiated
  *  by TxValidationState and BlockValidationState for validation information on transactions
  *  and blocks respectively. */
+template <typename Result>
 class ValidationState {
 private:
     enum mode_state {
         MODE_VALID,   //!< everything ok
         MODE_INVALID, //!< network rule violation (DoS value may be set)
         MODE_ERROR,   //!< run-time error
     } m_mode{MODE_VALID};
+    Result m_result{};
     std::string m_reject_reason;
     std::string m_debug_message;
-protected:
-    void Invalid(const std::string &reject_reason="",
+public:
+    bool Invalid(Result result,
+                 const std::string &reject_reason="",
                  const std::string &debug_message="")
     {
+        m_result = result;
         m_reject_reason = reject_reason;
         m_debug_message = debug_message;
         if (m_mode != MODE_ERROR) m_mode = MODE_INVALID;
+        return false;
     }
-public:
-    // ValidationState is abstract. Have a pure virtual destructor.
-    virtual ~ValidationState() = 0;
-
     bool Error(const std::string& reject_reason)
     {
         if (m_mode == MODE_VALID)
@@ -105,6 +106,7 @@ class ValidationState {
     bool IsValid() const { return m_mode == MODE_VALID; }
     bool IsInvalid() const { return m_mode == MODE_INVALID; }
     bool IsError() const { return m_mode == MODE_ERROR; }
+    Result GetResult() const { return m_result; }
     std::string GetRejectReason() const { return m_reject_reason; }
     std::string GetDebugMessage() const { return m_debug_message; }
     std::string ToString() const
@@ -121,36 +123,8 @@ class ValidationState {
     }
 };
 
-inline ValidationState::~ValidationState() {};
-
-class TxValidationState : public ValidationState {
-private:
-    TxValidationResult m_result = TxValidationResult::TX_RESULT_UNSET;
-public:
-    bool Invalid(TxValidationResult result,
-                 const std::string &reject_reason="",
-                 const std::string &debug_message="")
-    {
-        m_result = result;
-        ValidationState::Invalid(reject_reason, debug_message);
-        return false;
-    }
-    TxValidationResult GetResult() const { return m_result; }
-};
-
-class BlockValidationState : public ValidationState {
-private:
-    BlockValidationResult m_result = BlockValidationResult::BLOCK_RESULT_UNSET;
-public:
-    bool Invalid(BlockValidationResult result,
-                 const std::string &reject_reason="",
-                 const std::string &debug_message="") {
-        m_result = result;
-        ValidationState::Invalid(reject_reason, debug_message);
-        return false;
-    }
-    BlockValidationResult GetResult() const { return m_result; }
-};
+class TxValidationState : public ValidationState<TxValidationResult> {};
+class BlockValidationState : public ValidationState<BlockValidationResult> {};
 
 // These implement the weight = (stripped_size * 4) + witness_size formula,
 // using only serialization with and without witness data. As witness_size