Document message support for NaN and other special floating point numeric limits about ros2_documentation HOT 5 OPEN

And, the CLI also supports it on humble:
ros2 topic pub /ap/cmd_vel geometry_msgs/msg/TwistStamped "{header: {frame_id: base_link}, twist: {linear: {x: .nan, y: .nan, z: .nan}, angular: {z: 0.01}}}"

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Yeah, I think that is a reasonable thing to document; I'd enhance the table in https://docs.ros.org/en/humble/Concepts/Basic/About-Interfaces.html#field-types to add a "Note" column, or something like that. If you'd like to open a PR to add that, I'd be happy to review it.

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Yeah, I think that is a reasonable thing to document; I'd enhance the table in https://docs.ros.org/en/humble/Concepts/Basic/About-Interfaces.html#field-types to add a "Note" column, or something like that. If you'd like to open a PR to add that, I'd be happy to review it.

It doesn't look like it's actually supported.

In a .msg:

# NaN (IEE-754 quiet NaN) signifies no data is available at the location.
float64 my_value NaN

c: error: ‘nanl’ undeclared (first use in this function)

  276 |   msg->my_value = nanl;

c++: error: ‘nan’ was not declared in this scope

  198 |       this->my_value= nan;

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Relates to ros2/rosidl#705

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Huh, in the IDL 4.2 spec, it says nothing about special floating point values:
https://www.omg.org/spec/IDL/4.2/PDF

See section 7.2.6.4.

Then in the DDS Consolidated JSON 1.0 spec, it says that NaN is supported.
https://www.omg.org/spec/DDS-JSON/1.0/PDF
See section 7.3.7.4.8

Numeric values, such as Infinity, -Infinity, and NaN, which as stated in [ECMA-404] cannot be represented as
sequences of digits, shall be represented using the following JSON strings: "inf", "-inf", and "nan".

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