Azure Yaml DevOps variable handling - azure-devops

Question

So I have a YAML file where I am trying to do something like the following:
# top of the file, declare global variables
variables:
- name: MyName
value: 'apple'
...
parameters:
- name: SwitchName
type: boolean
default: false
...
stages:
- stage: Build
displayName: 'Build'
...
jobs:
variables:
- ${{ if eq(parameters.SwitchName, true) }}:
- name: MyName
value: '$(MyName)_pie'
...
steps:
- task: PowerShell#1
inputs:
scriptType: inlineScript
inlineScript: |
Write-Output $(MyName)
...
#end of script
The goal is to control the pipeline to print apple in default run and apple_pie when the user selects that parameter in the UI to be true.
I understand that parameters are compile-time and variables are run-time. I know that to overwrite a global variable you can create a variable at a job level and change it as yo see fit. Sadly, the way how template works do not let me redeclare that variable properly and I end up with $(MyName)_pie. For some reason, Yaml fails to see that inside that template there is a runtime variable that is needed to be defined.
What are my options here to achieve desired behavior?
Anything missing in my understanding here?

Answer 1

You can change to use the ${{ variables.MyName }} to call the variable in root level.
For example:
variables:
- name: MyName
value: 'apple'
parameters:
- name: SwitchName
type: boolean
default: false
stages:
- stage: Build
displayName: 'Build'
jobs:
- job: A
variables:
- ${{ if eq(parameters.SwitchName, true) }}:
- name: MyName
value: '${{ variables.MyName }}_pie'
steps:
- script: "echo $(MyName)"
Result:
Since you used an if expression to reassign value, the variable will be assigned at compile time.
Refer to this doc: Runtime expression syntax
You can use the template expression format: ${{ variables.var }}