Is it necessary that maintainer key always been a party?

Questions
2

edit: To the question in the subject, yes. Maintainers play a specific semantic role in the contract key model that may not simply be carried out by arbitrary data.

You need to tell DAML how to get the Partys from your CitizenKey.

If this is the only place, you could just write maintainer key._1.citizen.

If you generally want CitizenKey to work, you could add the missing instance. If I add this line to the file:

instance IsParties CitizenKey where

I get the error

Test.daml:63:10: error:
  • No explicit implementation for
  ‘toParties’
  • In the instance declaration for ‘IsParties CitizenKey’

So I can add

instance IsParties CitizenKey where
  toParties = ()

Now I get

Test.daml:64:15: error:
  • Couldn't match expected type ‘CitizenKey -> [Party]’
  with actual type ‘()’
  • In the expression: ()
  In an equation for ‘toParties’: toParties = ()
  In the instance declaration for ‘IsParties CitizenKey’

Now just implement that signature. There are a few ways; since what I want is “just recur on the IsParties instance for the citizen field”, I would write:

instance IsParties CitizenKey where
  toParties = toParties . citizen

But this is almost a stylistic choice at this point.

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