[BLO-137] ROS 2 [RFC]: Simpler primitive types for DataContainers

[IsabelParedes]

Context

Some frameworks and libraries use primitive Python and C types.

For instance, ROS 2 has a simple message specification¹.

Problem

Currently there is an impedance mismatch between Flojoy's DataContainers and those primitive Python and C types.

For instance, in the case of ROS 2, handling the standard libraries' messages in subscriber and publisher Blocks would be significantly more difficult. Primitive types need to be boxed behind subclasses of DataContainer, which would mean that one would have to create a plethora of DataContainer and adaptations.

Also if users were to define ROS 2 messages themselves for their application, they would need to define a custom DataContainer.

Another potential major project which is used in variety of applications to transfer data between stack and which would face a similar problem is [protobuf](https://protobuf.dev/).

Proposed Solutions

• have a generic ROS2Message subclass DataContainer:
  • pros:
    • would allow defining and using two Blocks for publishing and subscribing to ROS 2
  • cons:
    • make the underlying data opaque
    • would need Blocks to convert some DataContainer to/from ROS2Message
• allow Blocks to accept something else than DataContainer as inputs, e.g. simple Python list or tuple etc.
  • pros:
    • have the flexibility to pass simpler primitive types and containers from one Block to another
    • use the Python type annotation to perform type checking
  • cons:
    • potentially a lot more complexity to maintain overtime

References

• 1: ROS2 Message description specification
• 2: Protocol Buffers Documentation -- Overview

_{From SyncLinear.com | BLO-137}