When are data sections evaluated?

Question

When are PowerShell data sections evaluated?

Specifically, are they only ever evaluated once at the point of runtime definition/loading? Or are they evaluated on every execution of the containing function, even if it has already been defined/loaded?

I'm assuming that the containing context is a function or advanced function that will be called multiple times in a single session after being defined/loaded, rather than a script file that would have to be reloaded on every invocation (as far as I understand, anyway).

Answer 1

Script to test for both questions:

(get-date).TimeOfDay.ToString()
Start-Sleep -Milliseconds 100

DATA dat -supportedCommand Get-Date {
  get-date
}
Start-Sleep -Milliseconds 100

(get-date).TimeOfDay.ToString()
Start-Sleep -Milliseconds 100

$dat.TimeOfDay.ToString()

results (note that time from second line is the latest):

12:21:23.3191254
12:21:23.5393705
12:21:23.4306211

Which concludes that:

• Data section evaluation is executed immediately, not delayed
• Data section is evaluated only once, not on every usage

Data Sections would be much more useful if we had control over those mechanics. For example reading large text file only when needed or refreshing a variable upon every access.