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Konrad Grochowski commented on THRIFT-4060: ------------------------------------------- I do not completely follow your example: `set<detail::Lower>` will always contain `Lower`, even if you put `MyLower` there are you get is object splicing (http://stackoverflow.com/questions/274626/what-is-object-slicing). So there is no way for `MyHigher` to print out `MyLower` via `lowers`. So I'm not against introducing this annotation, but I'd like to see proper use-case :) (because for now all use-cases I see could rely on `printTo`, and it's better to keep thrift compiler simple - without too many annotations) > Thrift printTo ostream overload mechanism breaks down when types are nested > --------------------------------------------------------------------------- > > Key: THRIFT-4060 > URL: https://issues.apache.org/jira/browse/THRIFT-4060 > Project: Thrift > Issue Type: Bug > Components: C++ - Compiler > Affects Versions: 0.9.3, 0.10.0 > Environment: Ubuntu 14.04 LTS > Reporter: James E. King, III > Assignee: James E. King, III > > I'm in the middle of converting a project that provides some ostream > operators (for logging purposes) for a number of thrift structures. The > project was using 0.8.0 and in 0.9.3 some ostream operator overloads were > added with THRIFT-3336. The solution that was provided here runs into > complications if a thrift structure is contained within another one. Take > this simple example: > h4. Thrift > {noformat} > namespace cpp example.detail > struct Lower { > 1: binary lowerBinary > } > struct Higher { > 1: set<Lower> lowers > } > {noformat} > h4. C++ > {noformat} > namespace example { > class MyLower : public detail::Lower > { > virtual void printTo(std::ostream& os) const override; > } > class MyHigher : public detail::Higher > { > virtual void printTo(std::ostream& os) const override > { > os << lowers; > // here's the problem, lowers is a set<detail::Lower> when it > serializes in, > // not a set<MyLower>, so I cannot override it... > } > } > } > {noformat} > I'm considering adding an annotation to the thrift IDL that the compiler will > recognize that allows someone to say, "I am going to provide my own > operator<< for this structure, don't generate one". This would replace the > printTo mechanism that was added in THRIFT-3336. > Here is an example: > {noformat} > namespace cpp example.detail > struct MyLower { > 1: binary lowerBinary > } (cpp.customostream) > struct MyHigher { > 1: set<Lower> lowers > } > {noformat} > The annotation {{cpp.customostream}} (or the compiler option {{--gen > cpp:no_ostream_operators}} for global effect) tells the compiler to emit only > the declaration of the {{operator <<}} but does not emit a definition > (implementation). It would be up to the implementation building against the > generated code to provide an operator << if such an operator is needed for > conversion to a stream (cout, lexical_cast to string, etc..). -- This message was sent by Atlassian JIRA (v6.3.15#6346)