How should this Ansible variable be defined?

Question

I am trying to make sense of a variable reference I found in an incomplete Ansible role. The role references a value using

dest: “{{params['box'].t1}}”

In a separate yaml file I have

box:
    t1: "Albany"
    t2: "Albuquerque"

params isn't defined, so obviously this isn't going to work, but I can't figure out the correct way to define it. Can someone tell me where (or how) params must be defined for this variable reference to work in Ansible?

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Related questions. Does the use of square brackets in dest: “{{params['box'].t1}}” indicate that it is a dictionary? If yes, could I also write this as dest: “{{params['box']['t1']}” or dest: “{{params.box.t1}”?

Answer 1

params['box'].t1 refers to Albany in:

params:
  box:
    t1: "Albany"
    t2: "Albuquerque"

It is the same as params.box.t1 and params['box']['t1'].

Brackets refer to a key name, so they imply it is a dictionary.

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You typically use square bracket-notation when you want to refer to a key via a variable:

vars:
  wanted_key: box
  params:
    box:
      t1: Albany
    other:
      t1: Albuquerque

Then params[wanted_key].t1 refers to Albany.

In your example the value inside square brackets is a string (quoted), so all above examples are equivalent.