Support serialization as another type without casting

sipa · sipa · commit 818dc74ba274 · 2018-03-20T17:08:06.000-07:00
This adds a READWRITEAS(type, obj) macro which serializes obj as if it
were casted to (const type&amp;) when const, and to (type&amp;) when non-const.

This makes it usable in serialization code that uses a single
implementation for both serialization and deserializing, which doesn't
know the constness of the object involved.
diff --git a/src/addrman.h b/src/addrman.h
@@ -59,7 +59,7 @@ class CAddrInfo : public CAddress
 
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITE(*static_cast<CAddress*>(this));
+        READWRITEAS(CAddress, *this);
         READWRITE(source);
         READWRITE(nLastSuccess);
         READWRITE(nAttempts);
diff --git a/src/primitives/block.h b/src/primitives/block.h
@@ -93,7 +93,7 @@ class CBlock : public CBlockHeader
 
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITE(*static_cast<CBlockHeader*>(this));
+        READWRITEAS(CBlockHeader, *this);
         READWRITE(vtx);
     }
 
diff --git a/src/protocol.h b/src/protocol.h
@@ -349,7 +349,7 @@ class CAddress : public CService
         uint64_t nServicesInt = nServices;
         READWRITE(nServicesInt);
         nServices = static_cast<ServiceFlags>(nServicesInt);
-        READWRITE(*static_cast<CService*>(this));
+        READWRITEAS(CService, *this);
     }
 
     // TODO: make private (improves encapsulation)
diff --git a/src/script/script.h b/src/script/script.h
@@ -415,7 +415,7 @@ class CScript : public CScriptBase
 
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITE(static_cast<CScriptBase&>(*this));
+        READWRITEAS(CScriptBase, *this);
     }
 
     CScript& operator+=(const CScript& b)
diff --git a/src/serialize.h b/src/serialize.h
@@ -148,7 +148,12 @@ enum
     SER_GETHASH         = (1 << 2),
 };
 
-#define READWRITE(...)      (::SerReadWriteMany(s, ser_action, __VA_ARGS__))
+//! Convert the reference base type to X, without changing constness or reference type.
+template<typename X> X& ReadWriteAsHelper(X& x) { return x; }
+template<typename X> const X& ReadWriteAsHelper(const X& x) { return x; }
+
+#define READWRITE(...) (::SerReadWriteMany(s, ser_action, __VA_ARGS__))
+#define READWRITEAS(type, obj) (::SerReadWriteMany(s, ser_action, ReadWriteAsHelper<type>(obj)))
 
 /** 
  * Implement three methods for serializable objects. These are actually wrappers over
diff --git a/src/txdb.h b/src/txdb.h
@@ -46,7 +46,7 @@ struct CDiskTxPos : public CDiskBlockPos
 
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITE(*static_cast<CDiskBlockPos*>(this));
+        READWRITEAS(CDiskBlockPos, *this);
         READWRITE(VARINT(nTxOffset));
     }
 
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
@@ -395,7 +395,7 @@ class CWalletTx : public CMerkleTx
             mapValueCopy["timesmart"] = strprintf("%u", nTimeSmart);
         }
 
-        s << *static_cast<const CMerkleTx*>(this);
+        s << static_cast<const CMerkleTx&>(*this);
         std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev
         s << vUnused << mapValueCopy << vOrderForm << fTimeReceivedIsTxTime << nTimeReceived << fFromMe << fSpent;
     }
@@ -406,7 +406,7 @@ class CWalletTx : public CMerkleTx
         Init(nullptr);
         char fSpent;
 
-        s >> *static_cast<CMerkleTx*>(this);
+        s >> static_cast<CMerkleTx&>(*this);
         std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev
         s >> vUnused >> mapValue >> vOrderForm >> fTimeReceivedIsTxTime >> nTimeReceived >> fFromMe >> fSpent;
 

Original file line number	Diff line number	Diff line change
`@@ -93,7 +93,7 @@ class CBlock : public CBlockHeader`
`93`	`93`
`94`	`94`	`template <typename Stream, typename Operation>`
`95`	`95`	`inline void SerializationOp(Stream& s, Operation ser_action) {`
`96`		`- READWRITE(static_cast<CBlockHeader>(this));`
	`96`	`+ READWRITEAS(CBlockHeader, *this);`
`97`	`97`	`READWRITE(vtx);`
`98`	`98`	`}`
`99`	`99`
Original file line number	Diff line number	Diff line change
`@@ -349,7 +349,7 @@ class CAddress : public CService`
`349`	`349`	`uint64_t nServicesInt = nServices;`
`350`	`350`	`READWRITE(nServicesInt);`
`351`	`351`	`nServices = static_cast<ServiceFlags>(nServicesInt);`
`352`		`- READWRITE(static_cast<CService>(this));`
	`352`	`+ READWRITEAS(CService, *this);`
`353`	`353`	`}`
`354`	`354`
`355`	`355`	`// TODO: make private (improves encapsulation)`
Original file line number	Diff line number	Diff line change
`@@ -415,7 +415,7 @@ class CScript : public CScriptBase`
`415`	`415`
`416`	`416`	`template <typename Stream, typename Operation>`
`417`	`417`	`inline void SerializationOp(Stream& s, Operation ser_action) {`
`418`		`- READWRITE(static_cast<CScriptBase&>(*this));`
	`418`	`+ READWRITEAS(CScriptBase, *this);`
`419`	`419`	`}`
`420`	`420`
`421`	`421`	`CScript& operator+=(const CScript& b)`
Original file line number	Diff line number	Diff line change
`@@ -46,7 +46,7 @@ struct CDiskTxPos : public CDiskBlockPos`
`46`	`46`
`47`	`47`	`template <typename Stream, typename Operation>`
`48`	`48`	`inline void SerializationOp(Stream& s, Operation ser_action) {`
`49`		`- READWRITE(static_cast<CDiskBlockPos>(this));`
	`49`	`+ READWRITEAS(CDiskBlockPos, *this);`
`50`	`50`	`READWRITE(VARINT(nTxOffset));`
`51`	`51`	`}`
`52`	`52`
Original file line number	Diff line number	Diff line change
`@@ -395,7 +395,7 @@ class CWalletTx : public CMerkleTx`
`395`	`395`	`mapValueCopy["timesmart"] = strprintf("%u", nTimeSmart);`
`396`	`396`	`}`
`397`	`397`
`398`		`- s << static_cast<const CMerkleTx>(this);`
	`398`	`+ s << static_cast<const CMerkleTx&>(*this);`
`399`	`399`	`std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev`
`400`	`400`	`s << vUnused << mapValueCopy << vOrderForm << fTimeReceivedIsTxTime << nTimeReceived << fFromMe << fSpent;`
`401`	`401`	`}`
`@@ -406,7 +406,7 @@ class CWalletTx : public CMerkleTx`
`406`	`406`	`Init(nullptr);`
`407`	`407`	`char fSpent;`
`408`	`408`
`409`		`- s >> static_cast<CMerkleTx>(this);`
	`409`	`+ s >> static_cast<CMerkleTx&>(*this);`
`410`	`410`	`std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev`
`411`	`411`	`s >> vUnused >> mapValue >> vOrderForm >> fTimeReceivedIsTxTime >> nTimeReceived >> fFromMe >> fSpent;`
`412`	`412`