On Thu, 2018-03-15 at 15:54 -0400, Kim van der Riet wrote: > When creating an AMQP map body, using > > std::map<proton::value, proton::value> map; > > to represent the map, and once its values have been set, > > proton::message msg; > msg.body(map); > > is a convenient way to set the message body. However, in practice, I > am > finding this approach has one problem - I cannot guarantee the > key/value > ordering within the map.
Why do want to do this? > > On the receiving end, if I don't know the map keys in advance, I need > to > use a similar approach: > > std::map<proton::value, proton::value> map; > proton::get(msg.body(), map); > > which puts the map into a std::map where I can iterate through keys, > etc. But as soon as I do this, I have lost the ordering guarantees > of > the original message, as the map will iterate through the keys in an > internal order unrelated to the message ordering. > > What is the correct way to both set a proton::value as a map in such > a > way that the ordering is preserved when I both set the values and > read > them afterward without knowledge of the keys? I'm not sure what you are trying to accomplish, perhaps you can explain and that would make this easier to answer. Essentially though the AMQP concept of a map and language binding concepts of maps differ. They are just the closest most convenient things that allow users to accomplish what they most likely want to accomplish: That is to send an application level map/dictionary and receive it in a perhaps different language environment with the same meaning (more-or-less). As it happens std::map actually does have a well defined order (it is always ordered by the "less-than" relation on its keys) and I believe that the Qpid C++ binding coder will transcribe that into the AMQP map - this is not one of our tests though so it is entirely possible the iterator used goes backwards instead! However the map binding in other languages is much more likely to use the hash of the keys in the data structure and so there will be no well defined order for them. There are other "features" of AMQP maps that just aren't directly transcribeable to language features - especially if there are repeated identical keys in an AMQP map. Hope that helps Andrew --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@qpid.apache.org For additional commands, e-mail: users-h...@qpid.apache.org
