Support serialization as another type without casting

sipa · sipa · commit a6e5ddc0df2a · 2018-03-17T16:30:49.000-07:00
With the new AsType function it's possible to serialize an object as another
(compatible) type, and is intended for invoking the serializer of a parent
class.

Writing AsType&lt;Parent&gt;(child) will work in any context:
* READWRITE(AsType&lt;Parent&gt;(child))
* s &lt;&lt; AsType&lt;Parent&gt;(child)
* s &gt;&gt; AsType&lt;Parent&gt;(child)
In case child is const, the result will be a reference to a const
Parent type, resulting in const-correct behavior.
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));
+        READWRITE(AsType<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));
+        READWRITE(AsType<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));
+        READWRITE(AsType<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));
+        READWRITE(AsType<CScriptBase>(*this));
     }
 
     CScript& operator+=(const CScript& b)
diff --git a/src/serialize.h b/src/serialize.h
@@ -150,6 +150,12 @@ enum
 
 #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& AsType(X& x) { return x; }
+template<typename X> const X& AsType(const X& x) { return x; }
+template<typename X> X&& AsType(X&& x) { return std::move(x); }
+template<typename X> const X&& AsType(const X&& x) { return std::move(x); }
+
 /** 
  * Implement three methods for serializable objects. These are actually wrappers over
  * "SerializationOp" template, which implements the body of each class' serialization
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));
+        READWRITE(AsType<CDiskBlockPos>(*this));
         READWRITE(VARINT(nTxOffset));
     }
 
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
@@ -397,7 +397,7 @@ class CWalletTx : public CMerkleTx
             mapValueCopy["timesmart"] = strprintf("%u", nTimeSmart);
         }
 
-        s << *static_cast<const CMerkleTx*>(this);
+        s << AsType<CMerkleTx>(*this);
         std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev
         s << vUnused << mapValueCopy << vOrderForm << fTimeReceivedIsTxTime << nTimeReceived << fFromMe << fSpent;
     }
@@ -408,7 +408,7 @@ class CWalletTx : public CMerkleTx
         Init(nullptr);
         char fSpent;
 
-        s >> *static_cast<CMerkleTx*>(this);
+        s >> AsType<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`	`+ READWRITE(AsType<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`	`+ READWRITE(AsType<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`	`+ READWRITE(AsType<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`	`+ READWRITE(AsType<CDiskBlockPos>(*this));`
`50`	`50`	`READWRITE(VARINT(nTxOffset));`
`51`	`51`	`}`
`52`	`52`
Original file line number	Diff line number	Diff line change
`@@ -397,7 +397,7 @@ class CWalletTx : public CMerkleTx`
`397`	`397`	`mapValueCopy["timesmart"] = strprintf("%u", nTimeSmart);`
`398`	`398`	`}`
`399`	`399`
`400`		`- s << static_cast<const CMerkleTx>(this);`
	`400`	`+ s << AsType<CMerkleTx>(*this);`
`401`	`401`	`std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev`
`402`	`402`	`s << vUnused << mapValueCopy << vOrderForm << fTimeReceivedIsTxTime << nTimeReceived << fFromMe << fSpent;`
`403`	`403`	`}`
`@@ -408,7 +408,7 @@ class CWalletTx : public CMerkleTx`
`408`	`408`	`Init(nullptr);`
`409`	`409`	`char fSpent;`
`410`	`410`
`411`		`- s >> static_cast<CMerkleTx>(this);`
	`411`	`+ s >> AsType<CMerkleTx>(*this);`
`412`	`412`	`std::vector<CMerkleTx> vUnused; //!< Used to be vtxPrev`
`413`	`413`	`s >> vUnused >> mapValue >> vOrderForm >> fTimeReceivedIsTxTime >> nTimeReceived >> fFromMe >> fSpent;`
`414`	`414`