serialize: add SER_PARAMS_OPFUNC

Author: ajtowns

src/netaddress.h

@@ -218,6 +218,7 @@ class CNetAddr
     };
     struct SerParams {
         const Encoding enc;
+        SER_PARAMS_OPFUNC
     };
     static constexpr SerParams V1{Encoding::V1};
     static constexpr SerParams V2{Encoding::V2};

src/protocol.h

@@ -396,6 +396,7 @@ class CAddress : public CService
     };
     struct SerParams : CNetAddr::SerParams {
         const Format fmt;
+        SER_PARAMS_OPFUNC
     };
     static constexpr SerParams V1_NETWORK{{CNetAddr::Encoding::V1}, Format::Network};
     static constexpr SerParams V2_NETWORK{{CNetAddr::Encoding::V2}, Format::Network};

src/serialize.h

@@ -1192,4 +1192,17 @@ static auto WithParams(const Params& params, T&& t)
     return ParamsWrapper<Params, T>{params, t};
 }
 
+/**
+ * Helper macro for SerParams structs
+ *
+ * Allows you define SerParams instances and then apply them directly
+ * to an object via function call syntax, eg:
+ *
+ *   constexpr SerParams FOO{....};
+ *   ss << FOO(obj);
+ */
+#define SER_PARAMS_OPFUNC \
+    template <typename T> \
+    auto operator()(T&& t) const { return WithParams(*this, t); }
+
 #endif // BITCOIN_SERIALIZE_H