What is an "update" map mentioned in the Language basics:Maps section of the docs?

[benbfly]

The Language basics:Maps section of the docs has the following Tip:

Tip!: Appending an “update” map is a safer way to modify maps in Nextflow, specifically when passing maps through channels. This way, any references to the original map elsewhere in the pipeline won’t be modified.
https://www.nextflow.io/docs/latest/script.html#maps

I understand this to mean making a deep copy of a map rather than adding a new reference (which I agree can be important). Is this what was intended? Unfortunately, I can not figure out what the document means by an "update" map. I am not a native Groovy developer, but I searched the Nextflow documentation, google, ChatGPT, and the official Groovy Maps documentation (https://groovy-lang.org/groovy-dev-kit.html).

This tip should be clarified, perhaps with a link to the documentation for "update" maps?

[bentsherman]

It's not a technical term, that's why I put it in double quotes. Just an elaboration of the preceding example in which a map is updated by adding a new map instead of in-place mutation. See #2660 for the history behind this change. I think there was also a bytesize about it recently.

[benbfly]

I think I probably would have understood the meaning if the Tip had started:
"Appending an “update” map using the '+' operator as shown above is a safer way ..."

I also think you could add at the end of the tip: "This is especially useful in adding items to the 'meta' map, which is used extensively in nf-core" (since this is the map 90% of the users are going to be dealing with).

PS: I like the + operator! Somehow the solution I found online was to clone using meta.subMap(meta.keySet())

[pditommaso]

I agree with Ben, the overall tip is not clear at all. I think it should say "Creating a new map instance .." or "Cloning the map object " would be more precise