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https://issues.apache.org/jira/browse/THRIFT-4060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15862503#comment-15862503
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Konrad Grochowski commented on THRIFT-4060:
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ok, I did not get that {{MyHigher}} etc. was a try to override {{operator<<}}
behavior. Now I do see a need for such extension point :) But instead of
annotation (which makes .thrift file "language aware") I'd go with some
{{ifdef}} in generated source code. Something along
{{THRIFT_NO_GENERATED_OSTREAM_OPERATOR}} and {{ifndef}}. It would keep compiler
code simpler and (more importantly) service/data definition clean.
> 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..).
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