Hello,
Thanks for the answers.
Maybe I should give some more background on why this is of interest to
me. In RProtoBuf, we essentially only use the reflection api so that we
can dynamically load new proto message types at runtime, etc ... we
don't use protoc and therefore have no access to the generated classes.
In the class "GeneratedMessageReflection", there are templates such as :
template <typename Type>
inline Type GetRepeatedField(const Message& message,
const FieldDescriptor* field,
int index) const;
but they are private ? Why ?
From what I can read of the code, methods like GetRepeatedInt32 get
expanded out of :
PASSTYPE GeneratedMessageReflection::GetRepeated##TYPENAME( \
const Message& message,
\
const FieldDescriptor* field, int index) const {
\
USAGE_CHECK_ALL(GetRepeated##TYPENAME, REPEATED, CPPTYPE);
\
if (field->is_extension()) {
\
return GetExtensionSet(message).GetRepeated##TYPENAME(
\
field->number(), index);
\
} else {
\
return GetRepeatedField<TYPE>(message, field, index);
\
}
\
}
\
so doing things like this code
for( int i=0; i<size; i++){
INTEGER(res)[i] = (int) ref->GetRepeatedInt32( *message,
fieldDesc,
i ) ;
}
is going to be not as efficient as if I could directly iterate over the
repeated field using RepeatedField::iterator
Instead of extending the Reflection interface, what about making the
templates public in GeneratedMessageReflection and then maybe use some
sort of trait to indicate whether that the instance of Reflection I have
access to has these templates.
Something like :
template <typename _T, _T _V> struct integral_constant {
static const _T value = _V;
typedef _T value_type;
typedef integral_constant<_T,_V> type;
};
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
struct reflection_has_templates{} ;
struct reflection_no_templates{} ;
template <typename T> struct has_templates : public false_type{};
template<> struct has_templates<GeneratedMessageReflection> : public
true_type{} ;
So that using this trait, I can dispatch between :
- suboptimal implementation when the templates are not there
- optimal implementation using RepeatedField::iterator when they are
available.
It adds nothing to the Reflection interface.
Romain
On 02/12/2010 10:37 PM, Kenton Varda wrote:
Yeah, it would add a lot of complication and reduce the flexibility of
the Reflection interface. We don't want to require repeated fields to
be implemented in terms of RepeatedField or RepeatedPtrField.
On Fri, Feb 12, 2010 at 12:11 PM, Jason Hsueh <[email protected]
<mailto:[email protected]>> wrote:
+kenton
Kenton may have a better answer, but I surmise that it's to avoid
tying the Reflection interface to implementation details. A Message
implementation might not use RepeatedField at all. The original
version of protobufs used a different class to represent repeated
fields, so it wouldn't have been possible to implement Reflection
for the original version if the interface required access to
RepeatedField. So maybe the reason is historical. Recent changes
have been made that would make this technically possible. However,
adding methods to get direct access to the RepeatedField would still
expand the Reflection interface quite a bit. I'll defer to Kenton on
that.
On Fri, Feb 12, 2010 at 2:51 AM, Romain Francois
<[email protected]
<mailto:[email protected]>> wrote:
Why not ? It seems reasonnable to want to use e.g. std::copy and
friends.
On the documentation it says :
"
Most users will not ever use a RepeatedField directly; they will
use the get-by-index, set-by-index, and add accessors that are
generated for all repeated fields
"
What if I do want to use RepeatedField ?
Romain
On 02/11/2010 06:50 PM, Jason Hsueh wrote:
No, there isn't a way to get the RepeatedField from the
reflection
interface. You can only do so via the generated interface.
On Thu, Feb 11, 2010 at 5:57 AM, Romain Francois
<[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>> wrote:
Hello,
How can I get hold of a RepeatedField object to manage a
repeated
field in C++.
In RProtoBuf, we do a lot of :
for( int i=0; i<size; i++){
INTEGER(res)[i] = (int) ref->GetRepeatedInt32( *message,
fieldDesc,
i ) ;
}
where essentially the INTEGER macro gives a pointer to
the beginning
of the int array we are filling.
I'd like to replace this using e.g std::copy
RepeatedField field ;
std::copy( field.begin(), field.end(), INTEGER(res) ) ;
but I can't find how to actually get hold of a
RepeatedField object.
Is it possible ?
Romain
--
Romain Francois
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http://romainfrancois.blog.free.fr
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