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[REP-2011] Evolving Message Types #358
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df394d9
WIP
wjwwood c355ca6
still working
wjwwood 05ac47e
added more about the enforcing of the type versions
wjwwood 6dcb876
Increase readability, fix typos, and reduce ambiguities
methylDragon 42cf0de
Add clarification for field semantics
methylDragon d3449f0
Implement more fixups
methylDragon 98081d9
Methyl dragon/type description distribution (#2)
wjwwood d7628e7
rename from REP-2010 to REP-2011
wjwwood 22f6cb7
Add runtime type introspection section (#3)
methylDragon 8dccc0f
Add nested type description section (#4)
methylDragon b6a7086
Add alternatives and on_inconsistent_topic section (#5)
youliangtan a030033
fix rst errors, revise a few sections
wjwwood 04306e4
touch ups, rename to Run-Time Interface Reflection, reorganize
wjwwood d5e27d5
diagram typo
wjwwood fbc8810
fixup
wjwwood 01edda8
change title to a better wording
wjwwood 9ea2a20
fixups, reordering, tools section
wjwwood 24492e5
add feature progress section
wjwwood bd5cdbc
cleanup feature progress list
wjwwood ae78cf9
Update Type Version Hash to use SHA-256, and details updates based on…
emersonknapp ba2f96c
Update RIHS notes based on latest discussion (#8)
emersonknapp a4e1ef5
Remove Type Description/Hash content (moving to REP-2016) (#9)
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Update RIHS notes based on latest discussion (#8)
Signed-off-by: Emerson Knapp <[email protected]>
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Any consideration to be made on the max. lengths of the type names? Any restrictions to consider? Given the concatenated type version hash there might be little margin for using namespaces (which larger graphs tend to use).
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That's a good point, I suppose we'd have to consider the DDSI-RTPS spec that limits topic lengths to 256 characters...
Though, looking at what such a character length even looks like:
I think there's plenty of space for multiple nested namespaces? I'd imagine the type version hash wouldn't need more than 32 characters to have a relatively low chance of collision, but that's just a guess off the top of my head.
In which case a topic name would have 224 characters, which is still a lot.
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Also, since we're speaking about type names here (not topic names), the convention is to use
<package name>/<type, msg/srv/action>/<name>
, and so deeply nested namespaces isn't really as big of an issue as it is with things like topic names and node names.In table 9.12 of the DDSI-RTPS 2.2 spec (https://www.omg.org/spec/DDSI-RTPS/2.2/PDF) it says the type name is limited to 256 characters as well. So the limit is the same, but again, I don't think we're in danger here of running into this limitation in practical situations. At least not very often.
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One exception to this is the feature that allows you to configure topic endpoint's QoS using parameters: http://design.ros2.org/articles/qos_configurability.html
In this case the topic name is part of the parameter name, but unlike topic/service/node names, we don't have a limit for the length of parameter names at the moment.