with_nested on only one list

[Jerome Wagner]

Hello,

I don't know if this is normal (feature?) or if it can be considered as a bug that needs to be fixed :

- name: my task

  action: ...

  with_nested:

    - myList

does not loop over myList with each item referenced as item.0

I always have to go the "with_items: myList" and this breaks my workflow because 

 * when a task starts needing a nested loop all the item references need to be changed (from item to item.0 for instance).

 * I cannot copy/paste references between tasks using with_items and tasks using with_nested.

I can always write 

- name: my task

  action: ...

  with_nested:

    - myList

    - [ "" ]

but it feels clunky.

Has any of you encountered the same problem ?

[Michael DeHaan]

with_nested is intended to be iteration over two loops, a nested loop.

with_nested over a single list doesn't seem to make sense for me, you would just use "with_items".

A nested loop over *one* list offends my computer science sensibilities, and may also indicate a typo from the user, I don't think it should "just attempt to do something else" here.

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[Jerome Wagner]

Hello,

Sorry to insist here I thinks I understand the whole concept of nested loops ;-)

A nested loop over *one* item satisfies my sensibilities because, in this specific case, I feel it plays the same role as "0 for the addition" or "1 for the multiplication".

3 list case :

Loop

  Loop

    Loop

2 list case:

Loop

  Loop

1 list case:

Loop

It doesn't seem mis-behaved to be. 

The main reason I am insisting here is because with_items and with_nested lead to totally different referencing schemes for the items.

with_items:  {{ item }}

with_nested: {{ item.0 }}

which creates, in my viewpoint, non-necessary burden when you need to jump from a with_items scenario to a with_nested scenario and refactor a role.

Is there a way to do a with_items and still get the items as {{ item.0 }} ? maybe there is something I missed.

Thanks

[Michael DeHaan]

I understand what you are saying and that you understand what you are saying, I'm just not sure it's the best thing.

If someone types "with_nested" and only types one value, that's kind of a typo 99 times out of 100.

The idea that "I need to make a source control change to another line" seems minor in the grand scheme of things.

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[Jerome Wagner]

you encounter user problems everyday a lot more than me so if it is more harmful than beneficial on a usability perspective let's not do it !

I can very well live with

with_nested:

  - myList

  - [ "plug" ]

Let my explain a bit more my use case (which is not a simple source control problem).

Maybe I am the only one but tasks can rapidly become hard to read and hard to write because item.0, item.1,.. are not natural (at least to me)

so what I do is define in defaults/main.yml a set of macro accessors, like, for instance :

m_config: "{{ bundle[item[0]].item[1] }}"

and then in the roles I can simply use everywhere looping permits, m_config.key1, m_config.key2, ..

those "macro accessors" are very useful also when I need to re-organize the model of the datas because I usually simply have to change the macro definitions instead of going through the whole role.

My original post stemmed from the fact that with_items do not have the same references ({{ item }}) as with_nested ({{ item.0 }}) so the macro accessors cannot be shared between the with_items and with_nested cases.

I have a solution with the ["plug"], but the "one list" with_nested could have made this plug non-necessary.

Jerome

[Michael DeHaan]

My general theory is when something is hard to explain or hard for me to process, it's something hard, and we should avoid it.

That's been keeping us going for a while.

The idea of "macro accessors" is kind of doing that to my brain right now :)

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