What are the different between loop and with_items?

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Couuld you tell me What are the different between loop and with_items? and Which case we use loop which case we use with_items?

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with_items is the old way of doing it, see the loops documentation.

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short answer: loop is simple, with_X has magic, but in the end they do the same thing

long answer:

with_items is really loop + lookup('items'), so with_<any lookup can go here> is how loops worked, the items lookup has a implicit |flatten[1] filter so it is not exactly the same as loop: {{ lookup('items', mylist) }}, another lookup list is used for that aka with_list. A better example:

with_items:
        - [1,2]
        - [3,4]

will be a loop over 1,2,3,4:

 [started TASK: debug on localhost]
ok: [localhost] => (item=1) => {
    "msg": 1
}
ok: [localhost] => (item=2) => {
    "msg": 2
}
ok: [localhost] => (item=3) => {
    "msg": 3
}
ok: [localhost] => (item=4) => {
    "msg": 4
}

while:

# or with_list
loop:
        - [1,2]
        - [3,4]

will loop over 2 items each of them a list::

 [started TASK: debug on localhost]
ok: [localhost] => (item=[1, 2]) => {
    "msg": [
        1,
        2
    ]
}
ok: [localhost] => (item=[3, 4]) => {
    "msg": [
        3,
        4
    ]
}

This ‘magic’ lead to a lot of confusion with with_items and tthe other with_<<lookups>>, so loop was introduced to allow people to be able to use something simpler and less magical/hidden.

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