Allow constants

[tsujp]

Is your feature request related to a problem? Please describe.

In order to perform the features outlined in #3110 the concept of an explicit constant is required.

The following is currently invalid, and introducing constants would allow it to become valid:

var somethingAllowed = [
  'A'
  'B'
  'C'
]
@allowed(somethingAllowed)
param something string

// now somethingAllowed can be examined elsewhere (read-only)

Error

Error BCP032: The value must be a compile-time constant.

Referring to somethingAllowed within the decorator @allowed().

Also attempted hacks like array(somethingAllowed) etc do not work. It must be a literal.

Describe the solution you'd like

Addition of a const keyword, so now const somethingAllowed = [ ... ] defines an array which cannot be altered in any way and is guaranteed constant at compile time.

Giving:

const somethingAllowed = [
  'A'
  'B'
  'C'
]
@allowed(somethingAllowed)
param something string

// now somethingAllowed can be examined elsewhere (read-only)

[alex-frankel]

Variables are not allowed to be referenced in parameters, but I think this is one of those cases we can "fake" because we should be able to treat that var as a compile-time constant. @shenglol / @anthony-c-martin / @majastrz - any idea if we can enable this?

FWIW, a var in bicep is conceptually already a const since variables in bicep cannot be reassigned.

[majastrz]

Yup as long as the variable is a compile-time constant, it should be possible to inline it into parameters. (In the JSON, the value of the variable would be copied.)

(Separately, we'd probably need to rename the internal RequiresInlining flag because there are 2 different inlinings that would happen with basically opposite requirements.)

[shenglol]

Yeah it's possible to inline a constant, but I would like to point out that if we implement #622 and union type declaration, the const variable can be replaced with a type:

type SomethingAllowed = 'A' | 'B' | 'C'
param something SomethingAllowed
// Or just
param something 'A' | 'B' | 'C'

[ghost]

Hi tsujp, this issue has been marked as stale because it was labeled as requiring author feedback but has not had any activity for 4 days. It will be closed if no further activity occurs within 3 days of this comment. Thanks for contributing to bicep! 😄 🦾