DDS — DDS ISSUE# 54] Refactor or extend API used to access samples

Ref-74 Refactor_the_api_used_to_access_samples

The read() and take() operations return a "one-dimensional" array of
samples.

For the case where the PRESENTATION.access_scope==BY_INSTANCE and
either HISTORY.kind == KEEP_ALL or HISTORY.depth > 1 it is desirable
that the application can easily access all the samples that correspond
to one instance versus the samples that correspond to other
instances. For this purpose a 2-dimensional array (or sequence) where
a is preferable. That would allow for example to determine easily how
many samples are for each instance (before examining all) and also
easily examine the "first" or "last" sample of each instance without
navigating though all the other instances

What we would like is something like:

struct FooSample

;

typedef sequence<FooSample> FooSampleSeq;

read(out FooSampleSeq sample_seq);

typedef sequence<FooSampleSeq>; FooSampleCollatedSeq;

read_collated(out FooSampleCollatedSeq collated_seq);

Data would be then accessed as

sample_seq[i]->data;

Or else as

collated_seq[k][I]->data

However t is not clear how to map this to the IDL PSM.

**PROPOSAL**

No concrete proposal as it would be hard to represent in IDL but it
would be nice if such API was offered.

see below