ROS2 official parameter monitor example doesn't compile

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Thank you guys. I investigated and unfortunately I didn't find anything on the official DOC and repo about the accessibility of the Parameter Monitor in other versions different than Galactic, so your answer is right and yes, on my Galactic platfom I was sourcing Foxy, that's why I got the error.
I guess it is better to update the DOC section of Galactic about the Parameter Monitor saying that is exclusively available for Galactic because it's not mentioned (or I didnt see it....sorry if it's that)

It's probably not as visible as it should be, but: the tutorial you link to is not available for Foxy. If you search for it on the Foxy version of the documentation (selectable from the popup menu in the left bottom corner), you won't find it.

The indications you're looking at the "Galactic version":

and:

@gvdhoom sure, I wrote it in my answer, I know that the link points to Galactic and I tried to find it within the Foxy stuff and it's not available. Maybe just a line in the Galactic doc about this thing could be useful, just a suggestion. Anyway thank you so much about the speedy response, that's why I love this community.

I agree that sometimes you don't end up on the docs for the distro that your looking for. May I suggest you make a PR against ros2_documentation with the additional note, I'm sure it won't hurt anyone.