Hi,
I was porting session_services.cc to posix today, and I ran across a
g++ bug that will definitely block efforts to use CancelableRequest,
at least on Linux. While I'm savvy enough with C++, I'm having
trouble coming up with an explanation for what the problem is here.
I'd like to file a bug with gcc, but I don't want to just toss this
file on their laps. Can someone take a look at the test case I've
attached and see if they can shed some light? btw this test case
compiles successfully in visual studio.
$ g++ testcase.cc
testcase.cc: In constructor
'InternalGetCommandsRequest::InternalGetCommandsRequest(CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> >*)':
testcase.cc:89: error: class 'InternalGetCommandsRequest' does not
have any field named 'CancelableRequest'
testcase.cc:89: error: no matching function for call to
'CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >::CancelableRequest()'
testcase.cc:21: note: candidates are:
CancelableRequest<CB>::CancelableRequest(CB*) [with CB =
CallbackRunner<Tuple2<int, InternalGetCommandsRequest> >]
testcase.cc:13: note:
CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >::CancelableRequest(const
CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >&)
It seems that the critical point is:
no matching function for call to
'CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >::CancelableRequest()'
when the code in question is:
explicit InternalGetCommandsRequest(CallbackType* callback) :
CancelableRequest(callback) { }
For some reason, g++ is not picking up that we are passing a var of
type CallbackType* which fully translates to:
const CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >&
which would match the expected:
CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >::CancelableRequest(const
CancelableRequest<CallbackRunner<Tuple2<int,
InternalGetCommandsRequest> > >&)
Thanks,
James Hawkins
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class CancelableRequestBase {
public:
friend class CancelableRequestProvider;
CancelableRequestBase() {
}
virtual ~CancelableRequestBase() {
}
};
template<typename CB>
class CancelableRequest : public CancelableRequestBase {
public:
typedef CB CallbackType; // CallbackRunner<...>
typedef typename CB::TupleType TupleType; // Tuple of the callback args.
// The provider MUST call Init() (on the base class) before this is valid.
// This class will take ownership of the callback object and destroy it when
// appropriate.
explicit CancelableRequest(CallbackType* callback)
: CancelableRequestBase(),
callback_(callback) {
}
virtual ~CancelableRequest() {
}
private:
CallbackType* callback_;
};
template <class P>
struct TupleTraits {
typedef P ValueType;
typedef P& RefType;
typedef const P& ParamType;
};
template <class P>
struct TupleTraits<P&> {
typedef P ValueType;
typedef P& RefType;
typedef P& ParamType;
};
template <class A, class B>
struct Tuple2 {
public:
typedef A TypeA;
typedef B TypeB;
typedef Tuple2<typename TupleTraits<A>::ValueType,
typename TupleTraits<B>::ValueType> ValueTuple;
typedef Tuple2<typename TupleTraits<A>::RefType,
typename TupleTraits<B>::RefType> RefTuple;
Tuple2() {}
Tuple2(typename TupleTraits<A>::ParamType a,
typename TupleTraits<B>::ParamType b)
: a(a), b(b) {
}
A a;
B b;
};
template <typename Params>
class CallbackRunner {
public:
typedef Params TupleType;
virtual ~CallbackRunner() {}
virtual void RunWithParams(const Params& params);
};
// 2-arg implementation
template <typename Arg1, typename Arg2>
struct Callback2 {
typedef CallbackRunner<Tuple2<Arg1, Arg2> > Type;
};
class InternalGetCommandsRequest;
typedef Callback2<int, InternalGetCommandsRequest>::Type
InternalGetCommandsCallback;
class InternalGetCommandsRequest :
public CancelableRequest<InternalGetCommandsCallback> {
public:
explicit InternalGetCommandsRequest(CallbackType* callback) : CancelableRequest(callback) {
}
virtual ~InternalGetCommandsRequest();
};
int main(void)
{
return 0;
}
