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https://issues.apache.org/jira/browse/THRIFT-2220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13789142#comment-13789142
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Martin Vogt commented on THRIFT-2220:
-------------------------------------
Hello Jens,
>I probably just don't see it, but why do we need a new struct type?
I don't think that the struct has to be known in the IDL as new type.
But at least for the compiler/generator there has to be an
"escape identifier" to unmarshall the stream for a particular struct
with a factory helper.
For example I added in t_types.h two new methods set_is_base_Struct(bool flag)
and bool is_baseStruct(). This is currently set during the Thritfy.yy run.
During the generation this identifies the struct as a "virtual" struct. But
this can
be done (I think) with a name compare during the run of:
./thrift --gen cpp:base=TBase.
Then if a struct of this name is found it sets in t_types.h the flag and
then the generation behaves different.
I haven't looked at the source, but I think it can be done in the generator
alone.
regards,
Martin
> Add a new struct structv?
> -------------------------
>
> Key: THRIFT-2220
> URL: https://issues.apache.org/jira/browse/THRIFT-2220
> Project: Thrift
> Issue Type: Improvement
> Components: C++ - Compiler
> Affects Versions: 0.9.1
> Reporter: Martin Vogt
> Priority: Minor
>
> Thrift cannot extend structs, but maybe its possible to add a virtual base
> struct?
> Today I updated the "TBase" patch for gen cpp.
> https://issues.apache.org/jira/browse/THRIFT-1712
> After that, I modified the compiler to accept a new struct type, which
> describes that the marshalled struct needs to be created before the
> read(iproto) starts. (write already is fine, because on writing the
> specialized class is already created, only the "read" needs some factory, for
> the real implementation)
> For example:
> {code}
> struct_v TMVBase <<-- struct_v tell the generator to created the
> TBase class with a factory ("v"
> for virtual)
> service USB {
> void martin(1:TMVBase base);
> }
> {code}
> This is then generated into someting like this:
> {code}
> uint32_t USB_martin_args::read(::apache::thrift::protocol::TProtocol* iprot) {
> [...]
> switch (fid) {
> case 1:
> if (ftype == ::apache::thrift::protocol::T_STRUCT) {
> // TBase struct create:this->base
> this->base=TMVBase::create(iprot);
> xfer += this->base->read(iprot);
> this->__isset.base = true;
> } else {
> xfer += iprot->skip(ftype);
> }
> break
> [..]
> {code}
> This would allow to create the derived classed (from TBase) during marshall,
> without the need to define every method with any possible struct. Curently I
> have modified thrifty.yy and some other things, so that
> yacc actually parse this new "struct_v" type. But the generated source
> for it needs to be changed some more.
> The Protocolhandlers need to write the struct name on the
> wire, of course (which they currenty don' do).
> I think I can make a working prototype and post the patch.
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